SAMARRA, Iraq – U.S. troops raided two homes in this central Iraqi city this morning, arresting four family members of the most-wanted Iraq insurgent still at large.

The military said two of the detainees were suspected of keeping former Iraqi Vice President Izzat Ibrahim al-Douri in hiding. Al-Douri is believed to have been orchestrating continuing attacks against U.S. forces in Iraq.

Human Rights Watch, a top human rights group, had accused the U.S. military on Tuesday of committing war crimes by demolishing homes of suspected insurgents and arresting the relatives of Iraqi fugitives.

The military denied the charges, saying it only destroyed homes that were being used to store weapons or as fighting positions, adding that all Iraqis detained were suspected of taking part in attacks on coalition forces.

Also Tuesday, three Iraqi civilians were killed Tuesday, allegedly by U.S. gunfire, in the turbulent city of Fallujah after a protest over the detention of a teenage Iraqi girl.

And a U.S. Army Apache helicopter was apparently shot down Tuesday in the third such incident in two weeks. In this case, the crew members escaped without injuries.

The AH-64 helicopter gunship from the 3rd Armored Cavalry Regiment crashed near the town of Habbaniyah, military spokesman Col. William Darley said.

“It was apparently downed by enemy fire,” he said. The helicopter was covering a ground convoy moving in the area, the U.S. Central Command said.

In Fallujah, the civilians were shot after militants with rocket-propelled grenades fired at the city hall where some U.S. troops have offices, according to Iraqi police sergeant Nazar Yassin.

“The Americans responded by shooting indiscriminately,” said Yassin, who was on duty at the time and witnessed the incident.

Three people were killed and one was injured, Yassin said. Darley said he had no information on the incident.

As has often been the case, the violence this week was sparked by a house search and detention by U.S. troops.

In this instance, the situation was particularly sensitive because the person detained was a just-married 17-year-old girl. In Fallujah, a staunchly conservative Sunni Muslim-dominated town, such contact is a deep affront. Although the girl was accompanied and searched exclusively by women, according to a relative, the incident outraged townsmen.

In another incident Tuesday, grenade rounds were fired at a compound near Fallujah where ABC journalist Ted Koppel was reporting. U.S. soldiers returned fire, said Darley, the military spokesman.

Also on Tuesday, U.S. and United Nations officials said the U.N. will send a team of four military and security experts to Iraq within two weeks to prepare for the organization’s possible return to Iraq in support of the country’s transition to self-rule.

But senior U.N. officials cautioned that it is unlikely that the United Nations will play a major role in Iraq’s political transition until a new provisional government is established by June 30.