Prosecutors in Washington have charged a US citizen for joining the so-called Islamic State group in Syria, according to a statement from the Justice Department Wednesday. 

The charges allege that Lirim Sylejmani conspired to provide and provided material support to IS, which the United States has classified as a terrorist organization, between 2015 and 2019. 

The department also claimed he received military training from the self-styled caliphate. 

"The defendant is a U.S. citizen who abandoned the country that welcomed him to join ISIS in Syria," acting US Attorney Sherwin said in the statement of Sylejmani, who was born in Kosovo. "He will now be held accountable for his actions in an American courtroom."

Sylejmani was captured by the US-backed Syrian Democratic Forces (SDF) last year, according to the statement, before facing investigation by the FBI's Washington Field Office Joint Terrorism Task Force.

The question of how to handle captured foreign IS fighters has vexed Western governments, with the US vying for European countries to repatriate and try their own citizens. 

Nations such as France and Britain reject the return of battle-hardened supporters of the ultra-violent IS group, which has claimed responsibility for a slew of grisly attacks against civilians.

Some European governments, including Britain, have revoked the citizenship of a number of citizens over alleged IS links. 

But the US has pushed back against these approaches. 

"Leaving them in the desert is not an effective solution. It makes it more likely they're going to find their way back to the battlefield, and accepting that risk is not being tough on terrorism," the US State Department's counterterrorism coordinator Nathan Sales told a meeting in Brussels last year. 

Plus, it could put an undue burden on Middle Eastern countries already dealing with their own former IS-fighter citizens, according to the US. 

The EU-backed Genocide Network this spring advocated that returning IS foreign fighters should be charged with war crimes under international law -- such as genocide or crimes against humanity -- in addition to whatever terrorism charges they may face at home. 

As of May, some 2,000 fighters were still detained by Syrian forces and another 1,000 were in detention in Iraq, many of them European citizens mainly from France, Britain and Germany.