Insurgents hit a U.S. base in central Iraq with mortar shells, killing one American soldier and wounding two others, the military said Saturday. In a separate attack, rebels set off a bomb and opened fire on a U.S. convoy in Baghdad (search), killing two soldiers and wounding three.

Separately, British Prime Minister Tony Blair (search), President Bush's main ally in Iraq, made a surprise visit Sunday to southern Iraq to thank British troops for their part in the war.

Blair, whose political fortunes have wavered due to his backing of the U.S.-led campaign to topple Saddam Hussein (search), flew into Iraq's second-largest city by military aircraft from the Red Sea resort of Sharm el-Sheik, where he was on vacation with his family.

During the daylong visit, Blair was scheduled to meet military commanders and give a speech to some of the 10,000 British troops stationed in and around Basra (search).

The mortar shells struck a base of the Army's 4th Infantry Division on Friday night in Balad (search), north of Baghdad, Sgt. Robert Cargie said.

One shell exploded near a trailer used as a bedroom by some troops, and a soldier standing in its doorway was killed, he said. Two other soldiers were struck by shrapnel and taken to a combat support hospital, where they were in stable condition, Cargie said.

The U.S. military searched for the assailants by helicopter and set up checkpoints in the area. Six people were detained for questioning, a military spokesman said.

In a separate attack Friday in Baghdad, a bomb exploded in the al-Rashid district and insurgents opened fire on a U.S. convoy, killing two U.S. soldiers and wounding three others, the military said.

The names of the slain soldiers were withheld pending notification of next of kin.

Northwest of Baghdad, hundreds of residents protested Saturday in Hadithah, saying U.S. soldiers had raided the town overnight. A cameraman for Associated Press Television News filmed four shroud-covered bodies and one person in a hospital who was injured by a gunshot.

Residents said the four died in the U.S. raid, but there was no way to immediately verify the claim. The military had no immediate comment.

The soldiers were in armored vehicles and "targeted three houses — my sister's house, my uncle's and my own," said Abdel Meguid Awad, a resident.

Hadithah is part of the so-called "Sunni Triangle," the former heartland of Saddam Hussein's support and a center of opposition to the U.S.-led occupation. The American search for fugitives and insurgents is focused on the region.

Also Friday, the U.S. military shelled the sparsely populated southern edge of Baghdad to root out insurgents believed to be launching mortar shells and rockets.

A military spokesman said the shelling of the Doura neighborhood was part of an offensive dubbed Operation Iron Grip. Residents said it appeared U.S. fire was targeting fields in the neighborhood.

Bordered by date palm farms, Doura was once home to a number of former officials in Saddam's government and is now the site of a U.S. military base.

The military is conducting operations like Iron Grip "in response to mortar rounds being fired" from specific locations around the city, U.S. Army Brig. Gen. Mark Kimmitt told reporters.

The operations send "a very clear message to anybody who thinks that they can run around Baghdad without worrying about the consequences of firing (rocket propelled grenades), firing mortars," he said.