Two car bomb attacks killed at least 17 Iraqi security officers Saturday in the Sunni Triangle north and west of the capital, and two foreign truck drivers were fatally shot in the northern city of Mosul. A video posted on an Internet site purportedly showed extremists beheading a man accused of working with the Americans.

Six U.S. service members were wounded in a separate attack on a military convoy shortly after dawn in Baghdad.

The deadliest incident took place in Baghdadi, a city on the Euphrates River about 140 miles west of the capital. A suicide bomber detonated explosives in his vehicle outside a U.S. base guarded by Iraqi police, killing 16 Iraqi officers. A U.S. military spokesman said about 40 people were injured, none of them Americans.

A second car bomb killed one Iraqi National Guardsman at a checkpoint in the village of Ishaqi, located about 12 miles south of Samarra, a city that U.S. and Iraqi forces reclaimed from insurgents on Oct. 1. The Associated Press and Reuters reported a higher death toll, quoting police as saying that four guardsmen were killed in the incident.

The two truckers, a Turk and a Yugoslav, were gunned down as they drove through the center of Mosul.

An Internet video, purportedly posted by a group calling itself the Ansar al-Sunna Army, showed the beheading of a man it called a "crusader spy recruited by the Americans." Before he was executed, the victim identified himself as Seif Adnan Kanaan and said he was employed to deliver drinks to U.S. soldiers based at the airport in Mosul.

"I am telling anybody who wants to work with Americans not to work with them," the man said. "I found out the mujaheddin have very accurate information."

The U.S. military convoy in Baghdad was struck by a roadside bomb on the freeway leading to the city's airport, which is ringed by American bases. The explosion echoed across the city at 7:15 a.m., and a column of black smoke smeared the horizon.

News footage showed at least one armored vehicle in flames on what is widely regarded as the most dangerous road in the capital, because of frequent ambushes.

Also Saturday, Arabic-language satellite news networks aired appeals for the release of Margaret Hassan, an Irish-born humanitarian worker kidnapped this week. On Friday, Hassan, the Iraq country director for CARE, appeared on a videotape pleading tearfully for her life and urging Britain to break its alliance with U.S. forces in Iraq.

"It hurts to see my wife crying. We are in the holiest month of Islam," Tahseen Ali Hassan told al-Arabiya television network, referring to Ramadan. "I would like my wife to come back to me."

"She is a naturalized Iraqi citizen and always holds the people of Iraq in her heart," said Denis Caillaux, the secretary general of CARE International. "CARE joins with many of the people whose lives Mrs. Hassan has touched over her decades of service in Iraq in reaching out to her captors to appeal to their humanity."

In her videotaped plea, Hassan specifically urged Blair not to send British troops to the Baghdad area in a move that would free up U.S. forces for a threatened assault on Fallujah, a city about 35 miles west of the capital that has been under the control of Iraqi and foreign insurgents since April.

Iraqi officials said at a news conference Saturday that informal talks aimed at averting an offensive continued with leaders in Fallujah but that the effort remained hung up on the issue of foreign fighters allied with Abu Musab Zarqawi, a Jordanian-born militant who has asserted responsibility for many of the most violent attacks in Iraq. The officials also said airstrikes targeting gatherings of foreign fighters would continue, partly with the help of tips from Fallujah residents.

"The citizens are afraid of these beasts," said Hazim Shalan, Iraq's interim defense minister.

U.S. forces, meanwhile, continued operations around Fallujah. The military said Marines conducted a raid after midnight and apprehended a suspected aide to Zarqawi. Residents identified the man as Ghanim Mohammed Mohammedi, 37, an Iraqi who is a welder and former member of the Baath Party that governed Iraq under President Saddam Hussein.

The man's wife, Suad Fadhil, said he was captured while traveling from Fallujah to a home in the nearby city of Ramadi, where she had taken their three children to escape U.S. airstrikes that have driven most residents from the city.

"Yesterday I told him to go home to bring some winter clothes and some food for the end of Ramadan," she said. "I was shocked when I discovered he was arrested."

A man acting as mayor in the insurgent-controlled city, Mahmoud Ibrahim Jirisi, was also taken away by U.S. forces, but the circumstances were unclear. Jirisi's cousin, Hasan Ali Juraifi, said the mayor had met with the Americans outside town after receiving a call from them the previous night.

In Baghdad's Sadr City slum, Iraqi officials announced the final tally of a weapons-buyback program intended to disarm the Mahdi Army, a militia loyal to Moqtada Sadr, a rebellious Shiite cleric. Sadr has vowed to disarm and participate in politics, but U.S. officials remain wary of that pledge.

Iraqi officials said that $5 million had been paid out for 9,000 mines, 2,000 Kalashnikov assault rifles, 1,000 rocket-propelled grenades, 2,000 rocket-propelled grenade launchers and thousands of other munitions.

"The program was very successful, and the government has the intention of exporting it to other cities," said Barham Salih, the interim deputy prime minister.

In Najaf, 90 miles south of the capital, about 50 Iraqi security forces broke into Sadr's office and ordered it closed, according to Haider Turfi, an aide to the cleric. Turfi said no shots were fired but that both sides beat each other with weapons.

Special correspondent Saad Sarhan in Najaf contributed to this report.

Iraqi National Guardsmen arrive at the scene of a car bombing in the village of Ishaqi, north of Baghdad, that killed at least one National Guardsman. Another car bombing killed 16 Iraqi officers west of the capital.An Iraqi woman holds her wounded child at a hospital in Fallujah after their house was damaged in a U.S. airstrike in the insurgent-held city about 35 miles west of Baghdad.