The United States has voiced its concern after convicted terrorist Christodoulos Xeros went missing after a furlough from prison, urging Greek authorities to locate him and return him to prison.

Xeros was convicted in 2003, along with two of his brothers, of belonging to the November 17 urban guerrilla group, which killed 23 people – including foreign diplomats, policemen and businessmen – between 1975 and 2000. Xeros, who is serving six life sentences, vanished while on New Year's leave from Korydallos prison in Athens.

“We are deeply concerned that convicted terrorist Christodoulos Xeros, a central member of the 17 November terrorist organization that killed five US mission employees, is missing,” State Department spokeswoman Jen Psaki told journalists during a press briefing on Wednesday.

“We are engaged with Greek officials concerning this case. We call on the Greek Government to locate Xeros and return him to prison,” Psaki said.

“The United States and Greece are partners in combating terrorism in all its forms, and we work closely with Greek authorities in confronting those who use violence to seek to achieve their goals,” she said adding that November 17 was still on the list of the terrorist organizations of the State Department.

Meanwhile on Wednesday, Greek Justice Minister Haralambos Athanasiou called for the temporary suspension of 10 Korydallos Prison employees who had been on duty on December 31 following reports that Xeros held a party in the high-security jail with convicted members of another guerrilla group, Conspiracy of the Cells of Fire.

The staff are to remain suspended until a prosecutor probes the claims. Video footage from the prison on the night in question is to be scrutinized.