Agim Ceku was expelled from Colombia last month
A former Kosovo prime minister, Agim Ceku, has been arrested in Bulgaria on an international warrant issued by Serbia for alleged war crimes.
The Bulgarian interior ministry said Mr Ceku was detained as he crossed the border from Macedonia and a court would consider his case in the next few days.
Serbia accuses Mr Ceku of committing war crimes in 1998-99.
At the time he was commander of the ethnic-Albanian Kosovo Liberation Army (KLA), which was fighting Serbia.
The Serbian indictment accuses him of command responsibility for the murder of more than 600 Serbs.
He has dismissed the charges as politically motivated, and says the arrest warrant has no legal basis.
He was arrested at the Qustendil border crossing between Bulgaria and Macedonia on Tuesday evening.
Last month Mr Ceku was expelled from Colombia, after Serbia urged his arrest, but later he transited France en route to the Balkans.
He had previously been detained in 2006 in Slovenia and Hungary.
Kosovo declared independence in February 2008. Ethnic Albanians form the overwhelming majority of the population.
The US and more than 50 other countries have recognised its independence, but more than 100 have not, including Serbia and Russia.