PARIS/PRISTINA (Reuters) - French police on Wednesday arrested former Kosovo prime minister Ramush Haradinaj, a guerrilla commander during the 1998-99 Kosovo war, on a Serbian arrest warrant, French police sources and Kosovo’s Foreign Ministry said.

Ramush Haradinaj speaks during an interview with Reuters at the AAK headquarters in Pristina December 4, 2012. REUTERS/Hazir Reka

Serbia considers Haradinaj a war criminal for his role in leading a guerrilla insurgency in its former southern province of Kosovo, which declared independence with Western backing in 2008.

Haradinaj served briefly as prime minister of Kosovo in 2004 and 2005, while it was a ward of the United Nations, before being tried and acquitted twice of war crimes at a U.N. court in The Hague.

“He was stopped by French authorities based on an arrest warrant issued by Serbia in 2004 which for us is unacceptable,” Kosovo Foreign Ministry said in a statement.

The ministry said it was doing everything possible to secure his release, which it expected to happen.

French border police arrested him upon his arrival at Basel-Mulhouse airport in eastern France on a flight from Pristina, the sources said.

A French judiciary source said that investigators would on Thursday begin looking into whether there were reasons not to execute the extradition request, especially in the case that it had been issued for political reasons.

They would look at whether he had already been tried before the U.N. court on the same charges as those the arrest warrant had been issued on, the source added.

Haradinaj, the leader of the opposition party Alliance for the Future of Kosovo (AAK), was travelling on a diplomatic passport when he was stopped by French authorities.

In June 2015 Haradinaj was arrested by Slovenian police but was released after two days following diplomatic pressure.

Kosovo and France enjoy good diplomatic relations and Paris remains one of the biggest supporters of the youngest European state.