A man, who is not infected by coronavirus, lies on a bed at the emergency ward of a hospital which will be allocated for coronavirus patients in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. Picture taken March 29, 2020. REUTERS/Khaled Abdullah

A volunteer for a coronavirus awareness campaign wearing a protective face mask takes notes during a lecture in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 28, 2020. Picture taken March 28, 2020. REUTERS/Khaled Abdullah

Medical staff are pictured at a quarantine center built recently in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. March 29, 2020. REUTERS/Khaled Abdullah

An instructor addresses volunteers for a coronavirus awareness campaign in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 28, 2020. Picture taken March 28, 2020. REUTERS/Khaled Abdullah TPX IMAGES OF THE DAY

Medical staff are pictured at a quarantine center built recently in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. Picture taken March 29, 2020. REUTERS/Khaled Abdullah

A man wears a protective face mask as he leaves a hospital which is allocated for coronavirus patients in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. Picture taken March 29, 2020. REUTERS/Khaled Abdullah

A patient, who is not infected by coronavirus, lies on a bed at the emergency ward of a hospital which will be allocate for coronavirus patients in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. Picture taken March 29, 2020. REUTERS/Khaled Abdullah

Volunteers for a coronavirus awareness campaign attend a lecture in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 28, 2020. Picture taken March 28, 2020. REUTERS/Khaled Abdullah

Medical staff are pictured at a quarantine center built recently in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. Picture taken March 29, 2020. REUTERS/Khaled Abdullah

A medical appliance technician checks an out-of-service ventilator at an ICU unit of a hospital allocated for coronavirus patients in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. Picture taken March 29, 2020. REUTERS/Khaled Abdullah

Medical appliance technicians check an out-of-service ventilator at an ICU unit of a hospital allocated for coronavirus patients in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. Picture taken March 29, 2020. REUTERS/Khaled Abdullah

Medical staff are pictured at a quarantine center built recently in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020.Picture taken March 29, 2020. REUTERS/Khaled Abdullah

People leave a hospital allocated for coronavirus patients in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 29, 2020. Picture taken March 29, 2020. REUTERS/Khaled Abdullah

A volunteer for a coronavirus awareness campaign wearing a protective face mask attends a lecture in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 28, 2020. Picture taken March 28, 2020. REUTERS/Khaled Abdullah

Volunteers for a coronavirus awareness campaign wearing protective face masks attend lecture in preparation for any possible spread of the coronavirus disease (COVID-19), in Sanaa, Yemen March 28, 2020. Picture taken March 28, 2020. REUTERS/Khaled Abdullah

A Yemeni soldier looks at his mobile phone during a rally against the U.S. President Donald Trump's Middle East peace plan, in Sanaa, Yemen January 31, 2020. REUTERS/Mohamed al-Sayaghi

Bundles of Yemeni Riyal banknotes are pictured at the Central Bank of Yemen in Sanaa January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

Employees count bundles of newly issued Yemeni Riyal bank notes at the Central Bank of Yemen in Sanaa January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

Employees count bundles of Yemeni Riyal at the Central Bank of Yemen in Sanaa January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

An employee checks a bundle of Yemeni Riyal at the Central Bank of Yemen in Sanaa January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

Bundles of Yemeni Riyal banknotes are pictured at the Central Bank of Yemen in Sanaa January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

An employee takes bundles of Yemeni Riyal at the Central Bank of Yemen in Sanaa January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

Employees count bundles of Yemeni Riyal at the Central Bank of Yemen in Sanaa January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

Employees count bundles of newly issued Yemeni Riyal bank notes at the Central Bank of Yemen in Sanaa January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

Bundles of newly issued Yemeni Riyal bank notes are pictured at the Central Bank of Yemen in Sanaa, Yemen January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

An employee counts newly issued bundles of Yemeni Riyal at the Central Bank of Yemen in Sanaa, Yemen January 7, 2020. Picture taken January 7, 2020. REUTERS/Khaled Abdullah

Army officers and soldiers who have defected from the ranks of Yemeni government forces shout Houthi slogans during a ceremony held by the Houthis in Sanaa, Yemen December 29, 2019. REUTERS/Khaled Abdullah

Soldiers who have defected from the ranks of Yemeni government forces salute for the national anthem during a ceremony held by the Houthis in Sanaa, Yemen December 29, 2019. REUTERS/Khaled Abdullah

Southern Yemeni separatist security members patrol a road during a campaign to seize unlicensed motorcycles in Aden, Yemen December 10, 2019. REUTERS/Fawaz Salman

A southern Yemeni separatist security member checks a seized unlicensed motorcycle in Aden, Yemen December 10, 2019. REUTERS/Fawaz Salman

A southern Yemeni separatist security member stands by seized unlicensed motorcycles in Aden, Yemen December 10, 2019. REUTERS/Fawaz Salman

Southern Yemeni separatist security members check seized unlicensed motorcycles in Aden, Yemen December 10, 2019. REUTERS/Fawaz Salman

Southern Yemeni separatist security members patrol a street during a campaign to seize unlicensed motorcycles in Aden, Yemen December 10, 2019. REUTERS/Fawaz Salman

Southern Yemeni separatist security members patrol a street during a campaign to seize unlicensed motorcycles in Aden, Yemen December 10, 2019. REUTERS/Fawaz Salman

Southern Yemeni separatist fighters stand guard outside the headquarters of the Southern Transitional Council in Aden, Yemen November 5, 2019. REUTERS/Fawaz Salman

Yemeni people visit Dar al-Hajar tourist site in the outskirts of Sanaa, Yemen September 26, 2019. Picture taken September 26, 2019. REUTERS/Mohamed al-Sayaghi ?

Armed Houthi followers stand guard at the site of a rally to mark the 5th anniversary of the Houthi movement's takeover of the Yemeni capital Sanaa, in Sanaa, Yemen September 21, 2019. REUTERS/Khaled Abdullah

A Houthi follower shouts slogans as he attends a rally to mark the 5th anniversary of the Houthi movement's take-over of the Yemeni capital Sanaa, in Sanaa, Yemen September 21, 2019. REUTERS/Khaled Abdullah

Houthi followers rally to mark the 5th anniversary of their movement's takeover of the Yemeni capital Sanaa, in Sanaa, Yemen September 21, 2019. REUTERS/Khaled Abdullah

Houthi followers rally to mark the 5th anniversary of their movement's takeover of the Yemeni capital Sanaa, in Sanaa, Yemen September 21, 2019. REUTERS/Khaled Abdullah

Houthi followers rally to mark the 5th anniversary of their movement's takeover of the Yemeni capital Sanaa, in Sanaa, Yemen September 21, 2019. REUTERS/Khaled Abdullah

Houthi followers rally to mark the 5th anniversary of their movement's takeover of the Yemeni capital Sanaa, in Sanaa, Yemen September 21, 2019. REUTERS/Khaled Abdullah

Yemeni coast guards prepare to escort a tug boat ferrying members of a Houthi delegation to attend a meeting of a committee overseeing a U.N.-led peace deal that will be held on board a U.N.-chartered ship off Yemen's port city of Hodeidah September 8, 2019. REUTERS/Abduljabbar Zeyad

A Yemeni coast guard boat escorts a tugboat ferrying members of a Houthi delegation to attend a meeting of a committee overseeing a U.N.-led peace deal that will be held on board a U.N.-chartered ship off Yemen's port city of Hodeidah September 8, 2019. REUTERS/Abduljabbar Zeyad

Yemeni southern separatist leaders sit during a rally in support to the United Arab Emirates amid a standoff with the Saudi-backed government, in the port city of Aden, Yemen September 5, 2019. REUTERS/Fawaz Salman

Yemeni southern separatist leaders stand during a rally in support to the United Arab Emirates amid a standoff with the Saudi-backed government, in the port city of Aden, Yemen September 5, 2019. REUTERS/Fawaz Salman

Southern Yemeni separatist men guard a checkpoint in Aden, Yemen August 31, 2019. REUTERS/Fawaz Salman

Southern Yemeni separatist men are seen at a checkpoint in Aden, Yemen August 31, 2019. REUTERS/Fawaz Salman

A southern Yemeni separatist security member checks a car at a checkpoint in Aden, Yemen August 31, 2019. REUTERS/Fawaz Salman

A southern Yemeni separatist security member checks a truck at a checkpoint in Aden, Yemen August 31, 2019. REUTERS/Fawaz Salman

Southern Yemeni separatist men are see at a checkpoint in Aden, Yemen August 31, 2019. REUTERS/Fawaz Salman

A Southern Yemeni separatist security member checks a car at a checkpoint in Aden, Yemen August 31, 2019. REUTERS/Fawaz Salman

Honor guards carry the coffin of a Yemeni army officer killed in the southern province of Abyan in clashes with UAE-backed southern separatist forces, in Marib, Yemen, August 31, 2019. REUTERS/Ali Owidha

Mourners carry the coffin of a Yemeni army officer killed in the southern province of Abyan in clashes with UAE-backed southern separatist forces in Marib, Yemen, August 31, 2019. REUTERS/Ali Owidha

Yemeni army officers carry the coffin of a comrade killed in the southern province of Abyan in clashes with UAE-backed southern separatist forces, in Marib, Yemen, August 31, 2019. REUTERS/Ali Owidha

Honor guards carry the coffin of a Yemeni army officer killed in the southern province of Abyan in clashes with UAE-backed southern separatist forces, in Marib, Yemen, August 31, 2019. REUTERS/Ali Owidha

Yemeni army soldiers secure the site of a funeral for a Yemeni army officer killed in the southern province of Abyan in clashes with UAE-backed southern separatist forces, in Marib, Yemen, August 31, 2019. REUTERS/Ali Owidha

Mourners perform prayers during the funeral of a Yemeni army officer killed in the southern province of Abyan in clashes with UAE-backed southern separatist forces, in Marib, Yemen, August 31, 2019. REUTERS/Ali Owidha

Mourners perform prayers during the funeral of a Yemeni army officer killed in the southern province of Abyan in clashes with UAE-backed southern separatist forces, in Marib, Yemen, August 31, 2019. REUTERS/Ali Owidha