Bulgaria is to step up efforts to claim more than $20 billion compensation from Turkey for a refugee case dating back to 1913, an issue it says could hamper Turkish ambitions to join the European Union.

Government minister Bozhidar Dimitrov said on Tuesday Bulgaria's centre-right government, in office since July, would speed up the collection of documents so that it could submit its claim against Turkey by the end of the year.

Bulgaria is seeking compensation for the property of more than 250,000 Bulgarians forced out of their homes in eastern Thrace, now in Turkey, during the Balkan wars in 1913.

"Getting the compensation issue solved is one of the many conditions for Turkey to join the EU," Dimitrov told Reuters. "It is already in the EU's progress report on Turkey".

"Turkey has acknowledged the issue," said Dimitrov, who oversees the agency for Bulgarians abroad and the state archives. "It has not said it would not pay, but it wants to know exactly how much."

Turkey has expressed frustration over slow progress in its talks to join the 27-member EU, with one of the main problems a dispute with EU-member Cyprus.

Asked about reports on the compensation claim, Turkish Foreign Minister Ahmet Davutoglu called for officials to avoid remarks which could harm relations between the two countries.

"Turkish-Bulgarian relations have developed well enough to be a model for the region since the Cold War... What happened in history did not take the form of one-way migration," Davutoglu told a news conference.

"Two million Turks came from Bulgaria at that time... There is a great benefit in refraining from statements which would damage Turkish-Bulgarian friendship," he said.

Bulgaria joined the EU in 2007.

A Bulgarian-Turkish commission will convene once Bulgaria is ready to show concrete documentation and start talks on a settlement, Dimitrov said.

Some 2,300 documents have been collected but relatives of Bulgarian refugees are expected to present thousands more this year and that meant the claim was likely to exceed $20 billion, he said.

The compensation issue is likely to be discussed when Bulgarian Prime Minister Boiko Borisov visits Turkey in late January or early February, Dimitrov said.

Hundreds of thousands of ethnic Bulgarians were expelled from eastern Thrace, lying on the western side of the Bosphorus, in 1913. Turkey recognised the rights of the refugees in a 1925 treaty, but the agreement was never implemented, Dimitrov said.

(REUTERS)