Belgrade - Serbia will ask the United States to extradite an 86-year-old former member of a Nazi unit that killed thousands of civilians in a Belgrade death camp during World War II, an official was quoted Friday as saying.

US authorities took legal steps this week to revoke Peter Egner's citizenship, saying he concealed his service in the Einsatzgruppe unit after moving to the US in 1960.

"Once we collect enough material, we'll launch a formal investigation and seek his extradition," Bruno Vekaric, a spokesman for Serbia's war crimes prosecutor, told the Serbian daily Danas.

If Egner loses his citizenship, there would be no legal obstacles to returning him to Serbia to stand trial, Vekaric said.

US prosecutors allege that Egner, born in former Yugoslavia, volunteered for a Nazi-controlled police unit that killed 17,000 civilians mainly Serbs, Jews and Roma, at the Old Fairgrounds on the banks of the Sava river.

The US says he admitted last year to serving as a guard and an interpreter for the Belgrade-based unit from April 1941 to September 1943.

His service included a two-month period in early 1942 when the unit organized the killing of more than 6,000 people by asphyxiating them with exhaust fumes in a specially designed mobile van.

The US Justice Department this week asked a federal court in Washington state to revoke Egner's citizenship, saying he lied on his immigration form when he applied for citizenship in 1965 by omitting his involvement with Nazi police.

Egner lives in a retirement home in Bellevue, Washington. (dpa)