BAGHDAD, Iraq – A car bomb detonated by remote control exploded yesterday in Baghdad, killing two Iraqis but missing an American 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 January 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 suicide attacks at Shiite shrines.

Around dawn Friday, Defense Secretary Rumsfeld arrived in Mosul on a surprise visit to review Iraq security forces and meet with Iraqi and American leaders. Mr. Rumsfeld also made a surprise visit to Iraq on Christmas Eve.

The car bomb detonated on Tahrir Square 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, American military spokesman Lieutenant Colonel James Hutton said.

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

Most of the violence yesterday 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, 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 gun battle. Four insurgents also died in the fighting, the ministry said.

American troops evacuated some of the wounded, the American 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 Captain Ahmed Ismail said. Some of the trucks were owned by the government, Captain Ismail said.

Gunmen fired on an Iraqi police patrol yesterday in Baqouba, north of Baghdad, triggering a gun battle 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 yesterday 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 yesterday in clashes with American forces north of Ramadi, residents and hospital officials said.

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

A videotape obtained yesterday 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 February 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 an American 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 yesterday 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,” Mr. Ayar said. “This will lead to a little postponement in announcing the results.”