A battle between Pakistani security forces and suspected Islamic militants firing rockets and assault rifles left 21 dead Tuesday in a tribal region near the Afghan border.

The fighting was the latest in a spate of violence that has wracked the mountainous region in northwestern Pakistan, an area where fighters linked to the Al Qaeda terror network are believed to have taken refuge. In four clashes since Saturday, a total of 42 people have died.

The latest casualties came as militants fired rockets at a mountaintop military post in Sarbandki village in North Waziristan, a Pakistani official said. The official spoke on condition of anonymity because he was not authorized to speak to the media.

Troops returned fire, and the fighting continued intermittently for hours. Fourteen suspected militants -- including a local commander -- were killed in the clash, along with seven government soldiers, the official said.

Pakistan has placed about 70,000 troops and paramilitary forces along its border with Afghanistan to weed out alleged Al Qaeda and Taliban sympathizers and extremists.

Security officials have said hundreds of Arab, Central Asian and Afghan militants are in North Waziristan and South Waziristan, tribal regions bordering Afghanistan.

Last month, a senior Al Qaeda suspect from Egypt, Hamza Rabia, was killed in the area. Pakistan denied residents' claims that he died in a U.S. missile strike.

Violence flared again Saturday, when an explosion killed eight people at a cleric's home in Saidgi, a village in North Waziristan. Tribal leaders complained that U.S. helicopters launched the attack, landed and took off with five tribesmen.

The claim prompted a protest by Pakistan to the U.S. military.

Shortly after that explosion, suspected Islamic militants raided a checkpoint 30 miles away, killing eight Pakistani security forces.

Assailants in South Waziristan, meanwhile, ambushed and killed a pro-government tribal elder and four of his relatives, including a 5-year-old girl.

At least 60 tribal elders have been killed since they began cooperating with the Pakistani army after the Sept. 11 attacks in the United States.