A car bomb detonated by remote control exploded Thursday in Baghdad (search), killing two Iraqis but missing a U.S. military convoy as insurgent violence claimed more than 50 lives. Clashes between Iraqi police and rebels erupted along a major highway southeast of the capital.

With violence on the rise after the Jan. 30 election, Iraqi officials announced they would seal the country's borders for five days this month around a major Shiite religious holiday. Last year during the holiday, about 180 people were killed in attacks at Shiite shrines.

The car bomb detonated on Tahrir Square (search) in the heart of Baghdad, shattering the vehicle and setting several other cars on fire. At least two Iraqis were killed and two others were wounded, U.S. military spokesman Lt. Col. James Hutton said.

An American military patrol had just passed through the area but there were no U.S. casualties, Hutton said.

Most of the violence Thursday targeted Iraq's security forces, part of an apparent insurgent campaign to undermine public confidence after police and soldiers managed to prevent catastrophic attacks during the elections.

The biggest attack occurred in Salman Pak (search), 12 miles southeast of Baghdad, when insurgents attacked Iraqi policemen who came to look for weapons, showering them with machine-gun fire, rocket-propelled grenades and mortar rounds, police said.

Iraq's Interior Ministry said 14 policemen were killed, 65 were wounded and six were missing after the two-hour gunbattle. Four insurgents also died in the fighting, the ministry said.

American troops evacuated some of the wounded, the U.S. command said, and residents said American helicopters were prowling the skies.

"We were on patrol to search for weapons," wounded policeman Waad Jassim said from his hospital bed. "When we arrived, they opened heavy fire at us. There were many of them, and some were charging out of houses."

Elsewhere, bodies of 20 Iraqi truck drivers who had been shot were found dumped on a road, their hands bound behind their backs, police Capt. Ahmed Ismail said. Some of the trucks were owned by the government, Ismail said.

Gunmen fired on an Iraqi police patrol Thursday in Baqouba, north of Baghdad, triggering a gunbattle that killed a civilian and wounded two police officers, officials said. Assailants also killed a police lieutenant in Baqouba.

Five bodies in Iraqi National Guard uniforms were found Thursday in the insurgent stronghold of Ramadi, 70 miles west of Baghdad. Hospital director Ala al Ani said residents reported that the slain men were among 13 guardsmen who went missing recently. Two insurgents were killed Thursday in clashes with U.S. forces north of Ramadi, residents and hospital officials said.

A strong explosion shook the Rahmaniyah neighborhood of western Baghdad late Thursday, and residents said the blast occurred near a small Shiite mosque. Witnesses said there were casualties but police had no report.

A videotape obtained Thursday by Associated Press Television News showed gunmen killing four blindfolded men who identified themselves as Iraqi policemen. The video showed the four young men sitting cross-legged on the floor of a room. A date stamp on the video indicated it was recorded Feb. 3.

Several gunmen with assault rifles standing just steps away from the captives fired repeatedly at the men one by one, shooting them in the back of their heads.

Elsewhere, a body was found riddled with bullets in Mosul, and in the northern oil center of Kirkuk, a roadside bomb exploded several minutes after a U.S. military patrol passed, killing one Iraqi, police said. In Baghdad, gunmen shot to death a hospital receptionist.

Election officials had expected to release final results Thursday from the vote for a National Assembly, provincial councils and a regional parliament for the autonomous Kurdish north. On Wednesday, however, election commission spokesman Farid Ayar said the deadline would not be met because ballots in about 300 boxes had to be recounted.

"We don't know when this will finish," Ayar said. "This will lead to a little postponement in announcing the results."