During this time he was the military chief of the Kosovo Liberation Army, which consisted of ethnic Albanians and was, at the time, regarded as a guerilla group.

After the war, Ceku became a prominent figure in Kosovo, taking the Prime Minister's office in 2006 and actively promoting the region's independence.

Agim Ceku stepped down from the post last year – a month before Kosovo declared its independence.

“All the official bodies of the self-proclaimed Kosovo state include terrorists and bandits who had been in charge of the Kosovo Liberation Army. But NATO and the EU recognized them which, in essence, means they have pardoned them and Ceku, who is likely to escape unharmed again,” Serbia's parliament member Zoran Krasic.

Agim Ceku is not the only Kosovo figure to be accused of war crimes against Serbs. Several other leaders are also wanted by Belgrade, including Kosovo’s current Prime Minister Hashim Thaci.

Earlier this year Ceku was stopped in Columbia, but was simply expelled from the country. Few in Serbia expect that Bulgaria will allow Belgrade to try the former Kosovo Prime Minister.

Bulgaria is a NATO member, and one of more than 50 countries which recognize Kosovo as an independent state.

Members of Kosovo’s Social Democratic party, which Ceku heads, appear optimistic about their leader's fate.

“We expect him to be released soon but we don't know if that will happen tonight or tomorrow,” assured Gezim Kasapolli, spokesperson for Kosovo’s Social Democratic party.

Mr. Ceku is said to be held in custody in the Bulgarian city of Kyustendil on the west of the country where the local court will consider his case.

Ceku’s detention comes despite repeated demands from UN officials in Pristina that the Belgrade-issued warrant be dropped.

This is not the first time that Ceku has been detained. Three years ago he was arrested in Slovenia and later in Hungary, but both countries declined to hand him over to Serbia.

Last month Agim Ceku was deported from Colombia after he criticized Serbia for allegedly misusing its membership in Interpol.