Baghdad, Iraq ? Two car bomb attacks killed at least 22 Iraqi security officers on duty 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. Extremists also beheaded a man accused of working with the Americans, a videotape posted on the Internet showed.

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 similarly named capital. A suicide bomber exploded his vehicle outside a U.S. base guarded by Iraqi police, killing 16 Iraqi officers. About 40 people were injured, but a U.S. military spokesman said no Americans were among them.

A second car bomb killed one Iraqi national guard at a checkpoint near Samarra, a city in north-central Iraq that U.S. and Iraqi forces reclaimed from insurgent control on Oct. 1. News services reported a higher death toll, quoting police as saying four guardsmen were killed in the incident in the village of Ishaqi.

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

The Ansar al-Sunna Army group posted a videotape on the Internet showing 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,” Kanaan said. “I found out the mujaheddin have very accurate information … “

The U.S. 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 channels aired appeals for the release of Margaret Hassan, an Irish-born humanitarian worker kidnapped this week. On Friday, Hassan appeared on a videotape pleading tearfully for her life and urging Britain to break its alliance with U.S. forces in Iraq.