Four Iraqis were killed and nine hurt in a separate car bomb the same day.
BAGHDAD, Iraq (AP) -- Militants killed five U.S. Marines and authorities found 21 bodies Friday near the Syrian border, where American and Iraqi troops bore down in two recent major operations aimed at crushing a tenacious insurgency.
The victims, thought to be missing Iraqi soldiers, 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 Friday, a car bomb killed four men and wounded nine as they sat outside a restaurant in Baghdad waiting to pick up falafel sandwiches, a popular Arab staple made with fried chickpeas.
The bloodshed came as politicians seeking a negotiated solution to the insurgency once again wrangled over a promise to give Sunni Arabs a bigger say in charting Iraq's future.
The latest grim figures
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 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, haphazardly dumped by the roadside in a gravel pit and in sand flats. Three were beheaded and at least one had been mauled by animals.
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 Al-Qaida in Iraq to smuggle foreign fighters into the country.
"It's like the Mexican-American border there. There are attempts being made to seal it," a senior U.S. military intelligence official said on condition he remain unnamed for security reasons. The bodies were thought to be those of off-duty Iraqi soldiers who left their base near Qaim two days earlier in civilian clothes aboard two minivans, headed to Baghdad for vacation.
Marines carried out two operations in the area last month, killing 125 insurgents in the first campaign, Operation Matador, and 14 in the second, Operation New Market.