German prosecutors said Thursday they were probing whether purported CIA agents who allegedly kidnapped a radical Muslim cleric ever touched German soil, possibly widening a case that is already straining U.S.-Italy relations.

If prosecutors find the abductors touched German ground while passing through Ramstein Air Base (search) — considered U.S. territory — they will launch a formal inquiry that could lead to new charges, one said.

An Italian court has issued warrants for 13 purported CIA officials accused of helping carry out Osama Moustafa Hassan Nasr's (search) 2003 abduction, and is considering a prosecutor's request to issue arrest warrants against six more purported agents.

Nasr, known as Abu Omar, allegedly was snatched on a Milan street on Feb. 17, 2003, flown from Aviano to Ramstein air base in Germany, then to Egypt, where he reportedly was tortured.

The operation was said to be part of the CIA's "extraordinary rendition" program, in which terror suspects are transferred to third countries without court approval, subjecting them to possible ill-treatment.

Eberhard Bayer, a prosecutor in Zweibruecken (search), said his office is examining the route taken by the operatives. German authorities have asked their Italian counterparts for legal assistance and are investigating an unknown number of people for illegal restraint, constraint, and abduction, he said.

Nasr is believed to have fought in Afghanistan (search) and Bosnia (search), and Italian prosecutors were seeking evidence against him before his disappearance, according to Italian news reports last year, which cited intelligence officials.