Zimbabwean President Mugabe addresses the inaugural session of the World Summit on information society in Geneva, Switzerland, December 12, 2003. 

Chinese President Xi Jinping walks with Zimbabwean President Robert Mugabe (2nd L) upon arrival for a state visit in Harare, Zimbabwe December 1, 2015. REUTERS/Philimon Bulawayo 

Zimbabwe's President Robert Mugabe gives the speech he intended to make at parliament on Tuesday, at a hotel in the Zimbabwean capital Harare September 15, 2015. The 91-year-old president read out the wrong speech at the opening of parliament, an error which the main opposition quickly used to question whether Africa's oldest leader was still of a sound mind. REUTERS/Philimon Bulawayo 

Zimbabwe's President Robert Mugabe addresses the opening ceremony of the 24th Ordinary session of the Assembly of Heads of State and Government of the African Union (AU) at the African Union headquarters in Ethiopia's capital Addis Ababa, January 30, 2015. REUTERS/Tiksa Negeri 

Zimbabwe's newly sworn in Vice President Emmerson Mnangagwa (L) and President Robert Mugabe teach Daluthando Phelekezela Mphoko, 4, the ZANU PF salute at State House in Harare, December 12, 2014. REUTERS/Philimon Bulawayo 

Zimbabwe's President Robert Mugabe addresses supporters at the on going elective congress in Harare December 4, 2014. REUTERS/Philimon Bulawayo 

Zimbabwe's President Robert Mugabe and his wife Grace attend a Defence Force Day rally in Harare, August 12, 2014. Soon after being shoe-horned into the top ranks of Zimbabwe's ruling party, the wife of ageing leader Mugabe has earned a PhD, the latest sign she may be destined for high office in a country where the path to power is paved with academic letters. REUTERS/Philimon Bulawayo 

Zimbabwean President Robert Mugabe and Chinese Premier Li Keqiang (not pictured) during their meeting at the Great Hall of the People in Beijing, August 26, 2014. REUTERS/Diego Azubel/Pool 

Zimbabwe President Robert Mugabe attends the launch of basic commodities in Harare, July 16, 2008. Mugabe on accused Britain of trying to seize control of resources in the devastated African nation as his government announced inflation had risen to 2.2 million percent. REUTERS/Philimon Bulawayo 

Zimbabwe's President Robert Mugabe looks on during a rally marking Zimbabwe's 32nd independence anniversary celebrations in Harare April 18, 2012. REUTERS/Stringer 

Zimbabwe President Robert Mugabe speaks at a news conference following his party's election victory at the State House in Harare April 2, 2005. President Robert Mugabe's party scored an overwhelming win in Zimbabwe's parliamentary elections, taking the two-thirds majority it needs to ram through constitutional changes at will. REUTERS/Howard Burditt HB/TC 

Zimbabwe's President Robert Mugabe gestures at an election rally in the small town of Shamva northeast of the capital Harare, May 29, 2008. REUTERS/Philimon Bulawayo 

President of the Republic of Zimbabwe Robert Mugabe addresses at the 63rd United Nations General Assembly at U.N. headquarters in New York September 25, 2008. REUTERS/Eric Thayer 

Zimbabwe President Robert Mugabe inspects troops at the opening of Parliament in Harare, Zimbabwe, July 20, 2000. 

Zimbabwe's President Robert Mugabe (L) chats with Swaziland's King Mswati III during the annual Reed Dance at Ludzidzini in Swaziland August 30, 2010. REUTERS/Siphiwe Sibeko 

Zimbabwe's President Robert Mugabe (R) and his Equatorial Guinea counterpart Teodoro Obiang Nguema Mbasogo arrive for the opening of the Harare Agricultural Show, August 31, 2007. REUTERS/Philimon Bulawayo 

Zimbabwe's President Robert Mugabe (C) laughs with opposition leader Morgan Tsvangirai (L) and Arthur Mutambara, leader of breakaway faction of the main Zimbabwean opposition group Movement For Democratic Change (MDC), after signing a power-sharing deal at Rainbow Towers hotel in Harare September 15, 2008. REUTERS/Philimon Bulawayo 

Zimbabwe President Robert Mugabe lights the independence flame during the 29th Independence Celebrations at the National Stadium in Harare, April 18, 2009. Mugabe and his rival, Prime Minister Morgan Tsvangirai, celebrated independence from Britain together for the first time. REUTERS/Philimon Bulawayo 

Zimbabwe's President Robert Mugabe casts his vote as his wife Grace and daughter Bona (L-R) look on in Highfields outside Harare July 31, 2013. REUTERS/Siphiwe Sibeko 

Zimbabwe President Robert Mugabe and his wife Grace pay their respects at a funeral at the national shrine Heroes Acre November 28, 2003. REUTERS/Howard Burditt 

Zimbabwe's President Robert Mugabe (L) gestures as he arrives with his wife Grace for the annual conference of his ZANU-PF party in Gweru about 285 km (177 miles) west of the capital Harare, December 7, 2012. REUTERS/Philimon Bulawayo 

Zimbabwe's President Robert Mugabe (L) shares a light moment with his newly sworn-in Vice President John Nkomo (R) at the State House in the capital Harare December 14, 2009. REUTERS/Philimon Bulawayo 

President Robert Mugabe of Zimbabwe (R) holds hands with his South African counterpart Nelson Mandela greeting him on his arrival in the country in Harare, Zimbabwe, December 13, 1998. 

Queen Elizabeth II and the Duke of Edinburgh stand with the President of Zimbabwe, Robert Mugabe (L), shortly before he reviewed a guard of honour in London May 17, 1994. REUTERS/Kevin Coombs 

Libyan leader Colonel Muammar Gadaffi (L) and Zimbabwe President Robert Mugabe greet supporters outside State House in Harare July 12, 2001. 

President Robert Mugabe and new wife Grace leave the Kutama Catholic Church August 17, 1996 after exchaning their wedding vows. The couple were traditionally married shortly after the death of Mugabe's first wife Sally. The ceremony was attended by six thousand invited guests. REUTERS/Howard Burditt