Updated

Sunni clerics and Baghdad residents appealed on Friday for the release of an American and three other Christian humanitarian workers kidnapped by a group that has threatened to kill them.

The hostages — Tom Fox, 54, of Clear Brook, Va.; Norman Kember, 74, of London; and Canadians James Loney, 41, and Harmeet Singh Sooden, 32 — are members of the Christian Peacemaker Teams and were abducted in Baghdad on Nov. 26.

Sunni Arab clerics also took the opportunity of Friday's prayers to urge a big turnout in next week's elections, saying voting was a "religious duty" that could hasten the departure of American troops.

Sporadic violence left two people dead in Baghdad on Friday, one day after a homicide bomber detonated explosives inside a packed bus bound for the southern Shiite city of Nasiriyah, killing 32 people and wounding 44.

A U.S. military medical evacuation helicopter also made a "hard landing" in Tarmiyah 30 miles north of the capital. No one was injured.

The Canadian Islamic Congress sent an envoy, Ehab Lotayef, to Iraq to try to win the release of the humanitarian workers who were abducted two weeks ago. They include two Canadians and a Briton as well as the American.

A group known as the Swords of Righteousness has threatened to kill the four if U.S. and Iraqi authorities don't free all prisoners by Saturday.

A French aid worker and a German citizen are also being held by kidnappers.

During prayers in the al-Imam al-Aadam mosque in Baghdad's predominantly Sunni Arab neighborhood of Azamiyah in north Baghdad, cleric Ahmed Hassan demanded that the four charity workers be released.

"I stress on the necessity to release the four kidnapped foreigners who have helped the residents of Azamiyah," he said as residents held aloft protest banners.

Meanwhile, a statement posted on the Internet in the name of the Islamic Army in Iraq claimed to have killed another American hostage.

The statement Thursday did not name him or provide photos, but the group earlier identified its captive as Ronald Alan Schulz, 40, an industrial electrician from Alaska, and threatened to kill him unless all prisoners in Iraq were released.

U.S. and Iraqi officials have predicted a surge in insurgent attacks ahead of the Dec. 15 parliamentary elections. U.S. officials hope a large turnout, especially among Sunni Arabs, will help deflate the insurgency and lead to a reduction of American forces next year.

A Sunni cleric from the Association of Muslim Scholars told worshippers at Baghdad's Umm al-Qura mosque that a large turnout from the community was important.

The association is thought to have links to some groups in the Sunni-led insurgency, which had asked the minority to boycott last January's elections.

"The date of Dec. 15 is landmark event. It is a decisive battle that will determine our future. If you give your vote to the wrong people, then the occupation will continue and the country would be lost. Participation in the elections is a must and it is a religious duty," he said.

In Baghdad, police said a roadside bomb in the southern Dora neighborhood killed a police officer while another in western Saydiyah missed an American military patrol and killed an Iraqi passer-by.