Prosecutors in Kosovo have pressed terror charges against three alleged ISIS supporters, including two who went to the Syrian frontline to wage jihad, an official said Thursday.

The pair allegedly fought with the extremist group in Syria last year while the third "was propagating and recruiting people through Facebook to join IS [another term for ISIS]," Liridona Kozmaqi, spokeswoman of the chief prosecutor's office, told AFP.

The third was even "publicly inviting IS to liberate Kosovo", according to the indictment against him.

Kozmaqi said one of the men was out on bail while the other two were in detention. Their ages were not disclosed.

Muslim-majority Kosovo is home to 1.8 million people, around 300 of whom have joined the jihadists' frontlines in Iraq and Syria in recent years -- the highest ratio in any European country.

Kosovo's authorities have subsequently strengthened legislation and made high-profile arrests in a bid to root out suspected Islamist networks. They say around 50 homegrown jihadists have been killed in fighting while around 120 have returned to Kosovo.