Insurgents killed four U.S. soldiers in separate attacks Saturday, and U.S. officials announced the release of 238 detainees but said the move was unrelated to demands by the kidnappers of four Christian peace activists to free all prisoners.

Two of the soldiers were killed by small-arms fire southwest of the capital, the U.S. command said. The others died in a roadside bombing in Baghdad's Sunni Muslim neighborhood of Adhamiyah and by small-arms fire north of the city, according to the command.

The U.S. military also said a soldier was killed and 11 were wounded Friday in a suicide car bombing in the Abu Ghraib district of western Baghdad. That brought to at least 2,140 the number of U.S. military personnel who have died since the war began in March 2003, according to an Associated Press count.

Concern mounted over the fate of the four activists as a deadline set by kidnappers threatening to kill them passed Saturday.

The Interior Ministry said it had no information about the hostages -- Tom Fox, 54, of Clear Brook, Va., a town eight miles northeast of Winchester; Norman Kember, 74, of London; and two Canadians, James Loney, 41, and Harmeet Singh Sooden, 32 -- and emissaries from Canada and Britain showed no sign they had established contact with the kidnappers.

The previously unknown Swords of Righteousness Brigade seized the activists two weeks ago. It first set a deadline of Thursday but then extended it until Saturday, without giving a precise hour.

U.S. and British officials have expressed concern for the lives of the captives but made clear they would not bow to the kidnappers' demands.

On Saturday, U.S. officials said they had released 238 security detainees held by multinational forces in Iraq. However, such releases are common and arranged weeks in advance. U.S. Embassy spokeswoman Elizabeth Colton said the release was not in response to the kidnappers' demands.

The Reuters news agency reported from Baghdad:

With the election for seats in Iraq's first permanent government since the fall of Saddam Hussein less than a week away, candidates and campaigners came under fire across the country.

A former mayor in the southern Shiite holy city of Najaf said he survived an assassination attempt when a roadside bomb went off near his convoy, while in Mosul, in the north, gunmen shot two members of another party as they put up election posters, killing one and wounding the other.

The former mayor attacked in Najaf was Adnan Zurufi, an independent candidate in a city where political rivalry has boiled over as the vote draws near. "On my way back to my party office, a roadside bomb exploded targeting my convoy, wounding three of my guards," he said, blaming two political rivals but refusing to name them.

Members of the Quakers' Christian Peacemaker Teams hold a vigil in Toronto to support members held hostage in Iraq.