Insurgents killed four American soldiers in separate attacks Saturday as violence mounted five days ahead of national elections. U.S. officials announced the release of 238 detainees but said the move was unrelated to demands by 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 neighborhood of Azamiyah and by small arms fire north of the city, according to the command.

The U.S. military also said an American soldier was killed and 11 others 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 members 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 on Saturday. The Interior Ministry said it had no information about the hostages, and various emissaries sent 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 Thursday deadline but then extended it until Saturday, without giving a precise hour.

The four are Norman Kember, 74, of London; Tom Fox, 54, of Clear Brook, Va.; and Canadians James Loney, 41, and Harmeet Singh Sooden, 32.

Sunni Arab clerics used their main weekly religious service Friday to plead for the hostages' lives because of their humanitarian work and condemnation of the U.S.-led war in Iraq.

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 the multinational forces. However, such releases are common and arranged weeks in advance. U.S. Embassy spokesman Liz Colton said the release was not in response to the kidnappers' demands.

Elsewhere, the body of an Egyptian engineer was found Saturday, a day after he was seized by gunmen in Tikrit. Ibrahim Sayed Hilali had lived in Tikrit for a long time, police said.

A French aid worker and a German citizen also are being held by kidnappers. And there has been no further word on the fate of American hostage Ronald Allen Schulz, after an Internet statement in the name of the Islamic Army in Iraq on Thursday claimed his abductors had killed him.

Iraqi officials say the revival of foreigner kidnappings may be part of a bid to undermine Thursday's elections to choose a parliament for the next four years.

U.S. officials hope a big turnout among the Sunni Arab minority, the foundation of the insurgency, will help quell the violence so American and other foreign troops can begin withdrawing next year.

In an interview with AP, the top U.S. commander in Iraq said that based on the assessment of provincial governors, he expected a turnout Thursday of between 65 percent and 80 percent, "except in Anbar," the Sunni province most affected by the insurgency.

"We have seen a history of an increase in attacks heading up to the elections, leading into the referendums in an attempt to create the perception of insecurity to keep the Iraqi people from the polls," Gen. George W. Casey Jr. said. "They weren't able to do it in January ... and they're not going to be able to do it again."

The election commission, meanwhile, said Iraqis living abroad can begin voting Tuesday in the United States and 14 other countries. Officials estimate that about 1.5 million Iraqis live outside the country, although turnout among them was low in the January ballot.

Some insurgent groups, notably al-Qaida in Iraq, have warned voters not to participate in the election, although other Sunni insurgent groups have refrained from threats, raising hopes for a big turnout among the minority.

Elsewhere, a roadside bomb targeting a U.S. military patrol in Mosul killed two Iraqi civilians and wounded another. No American casualties were reported, said Bahaa al-Din al-Bakri, a doctor at Jumhouri hospital. Gunmen also killed a local aid official heading to work, al-Bakri said.

A prominent Sunni Arab candidate accused the Shiite-led government of withholding results of an investigation into torture allegations to avoid losing votes in the election. Saleh al-Mutlaq was referring to the discovery by U.S. troops last month of up to 173 malnourished Iraqi detainees at an Interior Ministry building in Baghdad.

On Nov. 15, Prime Minister Ibrahim al-Jaafari promised an investigation and results within two weeks. No report has been released. Al-Mutlaq urged an international investigation.

Al-Mutlaq also demanded that U.S. and Iraqi troops suspend raids and arrests in Sunni Arab areas so that Sunnis can vote Thursday.