The Bulgarian Supreme Prosecutor's Office of Cassation issued an order to keep former Kosovo PM, Agim Ceku, behind bars for another 72 hours.

Ceku was arrested by the Bulgarian authorities while trying to cross the border from the Serbian side and is being kept behind bars in the western city of Kyustendil.

The order was sent to the Regional Prosecutor's Office in Kyustendil and they will file Thursday a request with the Regional Court to keep Ceku for 40 days, which is the maximum legal period he can be held, despite Serbia's requests his immediate extradition.

Ceku is sought by Interpol for evading his 20-year jail sentence. The sentence was imposed by a Serbian Court over charges of genocide.

He was reported to Interpol by Serbian authorities on May 6.

Bulgaria's Prosecutor has requested from Interpol all materials on the case.

Agim Ceku has been Kosovo's PM from March, 2006 to January, 2008 in a coalition cabinet. He has been arrested twice - in 2003 in Hungary and 2004 in the Czech Republic, but was released over the immunity he had at the time. In May 2009, Ceku was expelled from an international conference in Colombia.

Ceku currently has no diplomatic immunity and entered Bulgaria for a private trip. Bulgaria's Foreign Ministry has denied he has been officially invited. Earlier on Wednesday Bulgaria's former Foreign Minister Solomon Passy said Akim Ceku came to Bulgaria at his invitation.

Before deciding to extradite him to Serbia, the Court in Kyustendil must rule if he had committed any crime according to the Bulgarian legislation and if he is indeed guilty of genocide, according to legal experts.

Serbia accuses Ceku of crimes against humanity including Serbs and people from other nationalities during the Kosovo War between 1998 and 1999.

At the time he was commander of the ethnic-Albanian Kosovo Liberation Army (KLA), which was fighting Serbia.

He has dismissed the charges as politically motivated, and says the arrest warrant has no legal basis.