The former prime minister of Kosovo, Agim Ceku, a former rebel commander wanted in Serbia on war crimes charges, has been arrested in Bulgaria, Bulgarian officials announced Wednesday. The Bulgarian Interior Ministry said Ceku had been detained based on an Interpol arrest warrant initiated by Serbia as he crossed the border from Macedonia on Tuesday. Kamen Mihov, a Bulgarian prosecutor in charge of international legal issues, said a court would decide by Friday whether to extend Ceku's detention by 40 days -- during which he could be extradited to Serbia -- or to release him. Serbia has accused Ceku of committing war crimes during the 1998-99 war in Kosovo, when he was a commander of the Kosovo Liberation Army, a rebel group that used guerrilla tactics to fight against Serbia's rule of Kosovo. The Serbian Justice Ministry said Ceku had been indicted in Serbia on charges of 'command responsibility' in relation to what it called the illegal deaths of 669 Serbs and 18 other non-Albanians in 1999. He has strenuously denied the accusations. Kosovo declared independence from Serbia in 2008. But Serbia, which regards Kosovo as its medieval heartland and is supported by Russia, has refused to recognize the country. Solomon Passy, the chairman of the Bulgarian parliament's foreign relations committee, called the arrest 'politically motivated.' Passy said he had invited Ceku to Bulgaria to discuss integrating Kosovo into international structures like the European Union and NATO. 'The decision of one parochial court does not represent the motivation of the international community,' he said. Ceku has not been indicted by the International Criminal Tribunal for the Former Yugoslavia in The Hague, but he has been arrested on two previous occasions on Interpol warrants, first in October 2003 at Ljubljana Airport in Slovenia, and then at Budapest Airport in February 2004. In both cases, he was released. He was also deported from Colombia in May 2009 on the basis of an Interpol warrant. Serbia insists that the extradition of Ceku is essential to achieve justice for atrocities against Serbs during the Balkan wars of the 1990s. But Balkan analysts said the arrest of Ceku, a prominent figure in Kosovo's struggle for independence, was also part of an effort by Belgrade to appeal to domestic public sentiment. The case is something of a difficult balancing act, however, because Serbia is also seeking closer ties with the European Union, and most of its member countries supported Kosovo's independence in the face of fierce Serbian resistance. 