A policemen was killed and three were injured Friday in Bulgaria as a standoff with a gunman who threatened staff and pupils at a nearby school turned deadly.

Petko Savov, 53, had barricaded himself in his flat in the northern town of Lyaskovets and was firing on police, said officials.

Bulgaria has identified a Lebanese man as the bomber who blew up an airport bus in 2012, killing five Israeli tourists, their Bulgarian driver and himself, local media said Sunday.

Israel and Bulgaria have already accused Hizbullah of being behind the attack at Burgas airport on the Black Sea, the deadliest on Israelis abroad since 2004.

Bulgaria's Socialists expelled former party chairman and the country's ex-president Georgy Parvanov on Friday, as a rift in the party's ranks grows ahead of European elections seen as crucial to the survival of the current government.

The expulsion of Parvanov and nine others came after the ex-leader said his newly formed Alternative for Bulgarian Revival (ABV) movement would run a separate list of candidates in the May vote for the Europeean Parliament.

A Bulgarian regional court said on Friday it had agreed to extradite a man wanted on terror charges in Germany.

Sulaiman Sidiqi, who was born in Kabul and has dual Afghan-German nationality, is suspected of being a member of "a terrorist organization", the Plovdiv Regional Court said in a statement.

Bulgaria's chief prosecutor says investigators have identified a fourth person they think was involved in the July 2012 bomb attack that killed five Israeli tourists and their Bulgarian bus driver.

Sotir Tsatsarov told reporters Thursday that because of the new evidence, the indictment will be delayed.

Bulgarian Prime Minister Plamen Oresharski survived a no-confidence vote in parliament on Wednesday, the third such motion against his cabinet put forward by the conservative opposition.

The motion, which failed in a vote of 116 to 93, claimed Oresharski has failed to reform the country's security sector and tackle an influx of over 11,000 refugees from Syria and elsewhere, among other criticisms.

Bulgaria's opposition party on Thursday put forward a third no-confidence motion against the country's Socialist-backed technocrat prime minister.

Plamen Oresharski took office last May, but quickly fell out of favor with disillusioned voters in the European Union's poorest country, who accused his government of corruption and links to the oligarchy.

Bulgarian President Rosen Plevneliev called Saturday for all the communist-era secret services' files to be opened immediately, still a controversial issue a quarter of the century after the collapse of the former regime.

"After 25 years, the time for keeping secrets has passed....All citizens, school pupils and students have the right to learn, with no intermediary, the truth about totalitarian power," he said in a national address.

German vice-chancellor Sigmar Gabriel on Saturday called for a debate on the touchy issue of immigration from poorer EU states Romania and Bulgaria.

"I think it's not necessary to exaggerate this issue. But it shouldn't be minimized either," he said in an interview with Bild newspaper.

European countries must stop returning asylum seekers to Bulgaria due to risks of "degrading" mistreatment there, the U.N. refugee agency said Friday, as Sofia struggles with an influx from war-torn Syria.

"Asylum-seekers in Bulgaria face a genuine risk of inhuman or degrading treatment due to systemic deficiencies in reception conditions and asylum procedures," said Babar Baloch, spokesman for the office of the U.N. High Commissioner for Refugees (UNHCR).