BAGHDAD, Iraq — Militants killed five U.S. Marines on Thursday — including a graduate of Seattle's Garfield High school — and authorities found 21 bodies yesterday near the Syrian border, where American and Iraqi troops bore down in two recent major operations aimed at crushing a tenacious insurgency.

Early today, a car bomb exploded in a street in a Shiite area of Baghdad, killing 10 people and wounding 27, police and hospital officials said today.

The dead Marine, Lance Cpl. Daniel Chavez, 20, was a tank crewman with the II Marine Expeditionary Force. Chavez was born in Odessa, Texas. He joined the Marine Corps on July 14, 2003, and deployed to Iraq in March. His awards include the National Defense Service Medal and the War on Terrorism Service Medal.

His family asked not to be contacted by reporters.

The Marines were killed Thursday in a roadside bombing while conducting combat operations near the volatile Sunni town of Haqlaniyah, 90 miles northwest of Baghdad, the military said. Their deaths brought to at least 1,689 the number of U.S. military members killed in Iraq since the war began in March 2003, according to an Associated Press count. At least 37 U.S. military members have been killed by roadside bombs since the makeup of Iraq's new government was announced April 28, according to the AP count.

The 21 bodies found yesterday were thought to be those of missing Iraqi soldiers, and were shot repeatedly in the head and found blindfolded, their hands tied behind their backs. Three were beheaded.

The killings were a clear sign of the profound difficulties faced by U.S. and Iraqi forces in Anbar province around the dusty, lawless frontier town of Qaim, and their inability to seal the porous desert border with Syria despite major efforts to boost their military presence in the area.

Also yesterday, a car bomb killed four men and wounded nine as they sat outside a restaurant in Baghdad. Gunmen killed the dean of the police academy in the southern city of Basra and an Iraqi soldier was killed by a roadside bomb in the central city of Mashru.

The 21 Iraqi bodies were found near Qaim, 80 miles west of Haqlaniyah, along a highway that meanders along the Euphrates River and into Syria. The bodies were in three locations.

U.S. military intelligence officials believe the Qaim area sits at the crossroads of a major route used by groups such as Abu Musab al-Zarqawi's group al-Qaida in Iraq to smuggle foreign fighters into the country.

The soldiers left their base near Qaim two days earlier in civilian clothes aboard two minivans, headed to Baghdad for a vacation.

Marines carried out two major operations in the area last month, killing 125 insurgents in the first campaign and 14 in the second. Eleven Marines were killed in the fighting, designed to scatter and eradicate insurgents using the road from Damascus to Baghdad.

As part of its effort to increase its presence, the Iraqi army boosted the number of soldiers at the frontier post of Akashat, near Qaim, from about 100 before the operations in May to nearly 750 now. Akashat is where the missing soldiers were based.

At least 91 car bombings, most carried out by suicide attackers, have been reported since Prime Minister Ibrahim al-Jaafari's Shiite-led government was announced on April 28, according to an AP count.

They are responsible for at least 291 of the nearly 900 Iraqis killed since then. The insurgent death toll is difficult to determine, but is thought to number more than 270.

Al-Qaida in Iraq claimed in an Internet posting that it abducted 36 Iraqi soldiers in western Iraq on Wednesday, and threatened to kill them unless al-Jaafari's government released "Muslim women" from prison.

In Baghdad, Iraqi politicians were divided over Iraqi President Jalal Talabani's promise to give Sunnis more seats on a 55-member committee drafting Iraq's first postwar constitution.

The charter must be ready to present to the 275-seat National Assembly by mid-August and will go before Iraq's voters in a referendum two months later. It requires the support of Sunnis — thought to make up 20 percent of the population.

Talabani's promise to raise the Sunni representatives from a proposed 15 to 25 — increasing the committee's size to 80 — averted a crisis after Sunnis threatened a boycott.

They renewed that threat yesterday if the Shiites and Kurds renege on the promise.

Seattle Times staff reporter Alex Fryer contributed information on Lance Cpl. Chavez. Associated Press reporter Mohammed Barakat contributed to this story from Qaim, Iraq.