A man walks near an archaeological site where a team led by Bulgarian professor Konstantin Totev found a gold reliquary cross in Veliko Tarnovo, Bulgaria, November 9, 2018. REUTERS/Stoyan Nenov

A gold reliquary cross, discovered during excavation works at an archaeological site at a medieval stronghold, is seen in Veliko Tarnovo, Bulgaria, November 9, 2018. REUTERS/Stoyan Nenov

Bulgarian professor Konstantin Totev poses for a picture at the archaeological site where a team led by Totev found a gold reliquary cross in Veliko Tarnovo, Bulgaria, November 9, 2018. REUTERS/Stoyan Nenov

A gold reliquary cross, discovered during excavation works at an archaeological site at a medieval stronghold, is seen in Veliko Tarnovo, Bulgaria, November 9, 2018. REUTERS/Stoyan Nenov

A gold reliquary cross, discovered during excavation works at an archaeological site at a medieval stronghold, is seen in Veliko Tarnovo, Bulgaria, November 9, 2018. REUTERS/Stoyan Nenov

A gold reliquary cross, discovered during excavation works at an archaeological site at a medieval stronghold, is seen in Veliko Tarnovo, Bulgaria, November 9, 2018. REUTERS/Stoyan Nenov

A supporter of Bulgaria's centre-right GERB party holds a poster of the party's leader Boiko Borisov during an election rally in the city of Veliko Tarnovo, about 250 km (160 miles) northeast of Sofia, May 10, 2013. Bulgaria's two main political parties, the GERB and the Socialists, were making their final attempts to woo frustrated voters before an election on Sunday that is likely to lead to a prolonged period of horse-trading to form a government. REUTERS/Stoyan Nenov (BULGARIA - Tags: POLITICS ELECTIONS)

Supporters of Bulgaria's centre-right GERB party cheer during an election rally in the city of Veliko Tarnovo, about 250 km (160 miles) northeast of Sofia, May 10, 2013. Bulgaria's two main political parties, the GERB and the Socialists, were making their final attempts to woo frustrated voters before an election on Sunday that is likely to lead to a prolonged period of horse-trading to form a government. REUTERS/Stoyan Nenov (BULGARIA - Tags: POLITICS ELECTIONS)

Supporters of Bulgaria's centre-right GERB party cheer during an election rally in the city of Veliko Tarnovo, about 250 km (160 miles) northeast of Sofia, May 10, 2013. Bulgaria's two main political parties, the GERB and the Socialists, were making their final attempts to woo frustrated voters before an election on Sunday that is likely to lead to a prolonged period of horse-trading to form a government. REUTERS/Stoyan Nenov (BULGARIA - Tags: POLITICS ELECTIONS)

Centre-right GERB party leader Boiko Borisov (C) is surrounded by bodyguards as he meets with supporters during an election rally in the city of Veliko Tarnovo, about 250 km (160 miles) northeast of Sofia, May 10, 2013. Bulgaria's two main political parties, the GERB and the Socialists, were making their final attempts to woo frustrated voters before an election on Sunday that is likely to lead to a prolonged period of horse-trading to form a government. REUTERS/Stoyan Nenov (BULGARIA - Tags: POLITICS ELECTIONS)

Centre-right GERB party leader Boiko Borisov (C) is surrounded by bodyguards as he meets with supporters during an election rally in the city of Veliko Tarnovo, about 250 km (160 miles) northeast of Sofia, May 10, 2013. Bulgaria's two main political parties, the GERB and the Socialists, were making their final attempts to woo frustrated voters before an election on Sunday that is likely to lead to a prolonged period of horse-trading to form a government. REUTERS/Stoyan Nenov (BULGARIA - Tags: POLITICS ELECTIONS)

Centre-right GERB party leader Boiko Borisov (C) meets with supporters during an election rally in the city of Veliko Tarnovo, about 250 km (160 miles) northeast of Sofia, May 10, 2013. Bulgaria's two main political parties, the GERB and the Socialists, were making their final attempts to woo frustrated voters before an election on Sunday that is likely to lead to a prolonged period of horse-trading to form a government. REUTERS/Stoyan Nenov (BULGARIA - Tags: POLITICS ELECTIONS)

Brazil's President Dilma Rousseff (C) and Bulgaria's President Georgi Parvanov (R) listen to a tour guide during their visit to the city of Veliko Tarnovo, some 220 km (137 miles) north-east of Sofia October 6, 2011. On the second day of her visit, Rousseff travelled to Veliko Tarnovo and the neighbouring mountain town of Gabrovo, east of capital Sofia, to meet distant relatives and see popular tourist attractions. REUTERS/Stoyan Nenov (BULGARIA - Tags: POLITICS SOCIETY)

Bulgarian army soldiers stand in formation near the Monument of Bulgarian Independence in the town of Veliko Tarnovo, some 220 km (137 miles) east from the capital Sofia, September 22, 2008. Bulgaria is celebrating the 100th anniversary of the country's independence from the Ottoman Empire. REUTERS/Oleg Popov (BULGARIA)

(L-R) Bulgaria's First Lady Zorka Parvanova, President Georgi Parvanov and Prime Minister Sergei Stanishev attend a ceremony at the Monument of Bulgarian Independence in the town of Veliko Tarnovo, some 220 km (137 miles) east from the capital Sofia, September 22, 2008. Bulgaria is celebrating the 100th anniversary of the country's independence from the Ottoman Empire. REUTERS/Oleg Popov (BULGARIA)

People hold a giant national flag of Bulgaria in the town of Veliko Tarnovo, some 220 km (137 miles) east from the capital Sofia, September 22, 2008. Bulgaria is celebrating the 100th anniversary of the country's independence from the Ottoman Empire. REUTERS/Oleg Popov (BULGARIA)

Bulgaria's President Georgi Parvanov places a wreath at the Monument of Bulgarian Independence in the town of Veliko Tarnovo, some 220 km (137 miles) east from the capital Sofia, September 22, 2008. Bulgaria is celebrating the 100th anniversary of the country's independence from the Ottoman Empire. REUTERS/Oleg Popov (BULGARIA)

Bulgarian army soldiers lay wreaths at the Monument of Bulgarian Independence in the town of Veliko Tarnovo, some 220 km (137 miles) east from the capital Sofia, September 22, 2008. Bulgaria is celebrating the 100th anniversary of the country's independence from the Ottoman Empire. REUTERS/Oleg Popov (BULGARIA)

Dutch Prime Minister Jan Peter Balkenende (R) listens to an orthodox
priest (L) at a church in the old part of the town of Veliko Tarnovo,
some 260km south from the capital Sofia, November 25, 2003. Balkenende
is in Bulgaria on a two-day official visit. REUTERS/Stoyan Nenov

SN/CRB

Dutch Prime Minister Jan Peter Balkenende (L) listens to a local guide
during his visit to the citadel Tsarevets in the town of Veliko
Tarnovo, some 260km south from the capital Sofia, November 25, 2003.
Balkenende is in Bulgaria on a two-day official visit. REUTERS/Stoyan
Nenov REUTERS

SN/

Bulgarian officials and journalists look at parts of destroyed Soviet-made Scud missiles in a factory near town of Veliko Tarnovo on September 1, 2002. The missiles destruction is a key pledge under Bulgaria's bid to join NATO but it has triggered concerns at home where people fear environmental damages. Bulgaria, which hopes to win an invitation for NATO at a Prague summit in the autumn, has pledged to destroy its Soviet-made missiles by end-October.

Bulgarian Defence Minister Nikolai Svinarov checks parts of destroyed Soviet-made SS-23 missile in a factory near the town of Veliko Tarnovo on September 1, 2002. The missiles destruction is a key pledge under Bulgaria's bid to join NATO but it has triggered concerns at home where people fear environmental damages. Bulgaria, which hopes to win an invitation for NATO at a Prague summit in the autumn, has pledged to destroy its Soviet-made missiles by end-October.

Bulgarian photographers take pictures of parts of destroyed Soviet-made SS-23 missile in a factory near town of Veliko Tarnovo on September 1, 2002. The missiles destruction is a key pledge under Bulgaria's bid to join NATO but it has triggered concerns at home where people fear environmental damages. Bulgaria, which hopes to win an invitation for NATO at a Prague summit in the autumn, has pledged to destroy its Soviet-made missiles by end-October.

Bulgarian officials and journalists look at parts of destroyed
Soviet-made Scud missiles in a factory near town of Veliko Tarnovo on
September 1, 2002. The missiles destruction is a key pledge under
Bulgaria's bid to join NATO but it has triggered concerns at home where
people fear environmental damages. Bulgaria, which hopes to win an
invitation for NATO at a Prague summit in the autumn, has pledged to
destroy its Soviet-made missiles by end-October. REUTERS/Dimitar
Dilkoff

Bulgarian Defence Minister Nikolai Svinarov checks parts of destroyed
Soviet-made SS-23 missile in a factory near the town of Veliko Tarnovo
on September 1, 2002. The missiles destruction is a key pledge under
Bulgaria's bid to join NATO but it has triggered concerns at home where
people fear environmental damages. Bulgaria, which hopes to win an
invitation for NATO at a Prague summit in the autumn, has pledged to
destroy its Soviet-made missiles by end-October. REUTERS/Dimitar
Dilkoff

Bulgarian photographers take pictures of parts of destroyed Soviet-made
SS-23 missile in a factory near town of Veliko Tarnovo on September 1,
2002. The missiles destruction is a key pledge under Bulgaria's bid to
join NATO but it has triggered concerns at home where people fear
environmental damages. Bulgaria, which hopes to win an invitation for
NATO at a Prague summit in the autumn, has pledged to destroy its
Soviet-made missiles by end-October. REUTERS/Dimitar Dilkoff

DD/