BAGHDAD — Five U.S. soldiers died in Iraq, the U.S. military announced today, a day after extremists fired shells into Baghdad's Green Zone during a visit by the State Department's No. 2 official.

Violence appeared mostly in check, but police said unknown bombers leveled a Sunni shrine near Basra, Iraq's second-largest city.

Three of the soldiers were killed when a bomb exploded near their vehicle Thursday during operations in Kirkuk province in northern Iraq, the U.S. military said in a statement. Another soldier was wounded in the blast.

A fourth soldier was killed by small arms fire the same day in Diyala province, northeast of Baghdad, another statement said. And another soldier died Wednesday in a non-combat related incident, which the military said it was investigating.

A curfew remained in place in the capital two days after suspected al-Qaida bombers blew the minarets off a sacred Shiite shrine in Samarra and stoked fears of a bloody sectarian backlash.

Gunmen armed with rocket-propelled grenades attacked the Talha Bin al-Zubair shrine late Thursday, partially damaging the building, police said. They returned early Friday, planting bombs inside the structure and exploding it completely, police said. No injuries were reported.

Gen. Ali al-Mussawi, a top Basra security official, said the bombers were disguised as cameramen who asked guards for permission to film inside the shrine. Minutes after they left, a huge explosion rocked the building, destroying the dome and minaret, he said.

The guards were detained afterward for questioning, al-Mussawi said.

Talha Bin al-Zubair was one of the Prophet Muhammad's companions, and commands high respect among Sunnis. The shrine was renovated in late 1990s and during Saddam Hussein's rule, Sunni pilgrims from India, Pakistan and Turkey frequently made pilgrimages to the site.

At least four Sunni mosques were attacked within hours of the Shiite shrine blasts in Samarra on Wednesday, and police in Basra reported four people killed in retaliatory violence there.

Thursday's barrage of rockets and mortars included one that hit on a street close to the Iraqi parliament less than a half hour before Deputy Secretary of State John Negroponte passed nearby.

The attack again showed militants' resilience — including their ability to strike the heavily protected zone — despite a U.S.-led security crackdown across the city that began four months ago. But officials paid much closer attention to any signs that Shiites could unleash another wave of retaliation against Sunnis for the explosions at the Askariya mosque compound in Samarra.

The first attack on the site in February 2006 sent the country into a tailspin of sectarian violence that destroyed Washington's hopes of a steady withdrawal from Iraq. On Wednesday, bombers toppled the two minarets that stood over the ruins of the mosques famous Golden Dome about 60 miles north of Baghdad.