Four U.N. police officers from Jordan (search) were stripped of their diplomatic immunity Monday to be questioned in a fellow Jordanian's killing of two American guards in Kosovo.

It wasn't clear why Sgt. Maj. Ahmed Mustafa Ibrahim Ali (search) opened fire on a convoy of corrections officers on Saturday. He and the two female American guards were killed in the shootout that followed, and 11 people were wounded.

Ali was a member of a highly trained unit in Jordan and had been decorated for warding off an attack on the Israeli Embassy in Amman (search), a Jordanian official said.

The four other Jordanian police officers at the prison in the town of Kosovska Mitrovica were detained. Authorities lifted their diplomatic immunity, opening the way for them to be interrogated, officials said.

A delegation of Jordanian police officials arrived Monday in Kosovo (search) to assist with the investigation, which is led by an international prosecutor, officials said.

Eight of the 10 Americans were moved to a U.S. military base in Kosovo for treatment, a U.S. military spokesman said Monday. The other two were treated and released, and an Austrian also wounded was flown home Sunday for treatment.

One American officer remained in critical condition following brain surgery in neighboring Macedonia, U.S. peacekeeping spokesman Staff Sgt. Michael Houk said.

The attack shook the United Nations mission in Kosovo, already in turmoil following violent ethnic clashes last month between ethnic Albanians and Serbs that killed 19 and wounded more than 900 in Kosovska Mitrovica.

"The shooting struck a huge blow at the very idea of peacekeeping," said Alex Anderson, the Kosovo project director of the International Crisis Group, a Brussels-based organization that monitors the Balkans.

An American police officer serving with the U.N. mission in Kosovo told The Associated Press that the shooting was "clearly an attack against Americans." The officer spoke on condition of anonymity.

Officials denied rumors that a quarrel about the war in Iraq had sparked the gunbattle.

"As far as we know, there was no communication between the officer who fired and the group of victims," said Neeraj Singh, a U.N. spokesman.

The officers were part of the U.N. mission that has administered Kosovo and provided security since June 1999, when Belgrade's authority over the province was removed following a NATO air war that stopped a Serb crackdown on independence-seeking ethnic Albanians.

"This is a sad day for United Nations peacekeeping," said Stefan Feller, the head of the U.N. police in Kosovo. "At this stage there can be no conclusions on the reason for the shooting."

The gunbattle began as three U.N. vehicles carrying 21 U.S. correctional officers, two Turkish officers and the Austrian were leaving the prison, which was guarded by five Jordanian special police unit officers, officials said. The correctional officers, who arrived in Kosovo just 10 days ago, had been training at the prison.

Ali, 30, started firing at the convoy, Feller said, and the officers returned fire.

Jordan's government expressed regret for the shootings, a statement carried by the official Jordanian Petra agency said.

The slain Americans were identified as Kim Bigley, 47, of Paducah, Ky., and Lynn Williams, 48, of Elmont, N.Y., said Mike Dickerson, spokesman for Computer Sciences Corp. Both worked for Dyncorp, a susidiary of CSC that trains police, corrections and judicial for overseas duty.

The 3,500-strong U.N. police force includes 450 U.S. officers, most of whom work for Dyncorp. The U.N. police force works alongside 6,000 local police officers.