Up to 50 Pakistani troops were missing amid fierce fighting Monday with pro-Taliban militants near the Afghan border that has already left scores dead, the army said.

The troops disappeared after militants attacked security posts and a foot patrol near the town of Mir Ali in the North Waziristan region, an army statement said.

The fighting comes as Gen. Pervez Musharraf tries to secure another term as president vowing to shore up Pakistan's troubled effort against Islamic extremism.

It also coincides with a change of command in the Pakistani army, which is suffering heavy losses in an escalating confrontation with militants who have seized control of swaths of territory near the frontier.

The army said earlier that about 60 suspected militants and 20 soldiers had died in two major clashes in North Waziristan on Sunday.

A security official in Miran Shah, the region's main town, said army helicopters and jets bombarded militant positions in several villages in the region.

He said informers had told security forces that two Arabs who were low-ranking al-Qaida men and an Uzbek died in the second battle in an area called Malagam.

About a dozen civilians, including women and children, died when a stray mortar struck their home in Mir Ali, said the official, who spoke on condition of anonymity because he was not authorized to speak to the media. It was unclear who fired the mortar.

Asked about reported civilian deaths on Geo television on Monday, army spokesman Maj. Gen. Waheed Arshad said security forces had fired only at targets from which they were being attacked.

Some residents fleeing villages located near Mir Ali were arriving in Miran Shah on Monday.

"Oh God! Kill those who killed our innocent people and made us homeless," said Ahsan Ullah. He said about 300 people had left the area.

Pakistan sent troops into its rugged, semiautonomous frontier region for the first time after Taliban and al-Qaida militants took refuge there from the U.S.-led invasion of Afghanistan in 2001.

On-off fighting has killed hundreds of Pakistani troops and militants and flared again in July after the army stormed a radical mosque in the capital, Islamabad, and sent more forces into the border region.

Despite the fighting, American officials who count Musharraf as a key counterterrorism ally claim the area has become a safe haven for al-Qaida and a rear base for Taliban guerrillas fighting NATO troops in Afghanistan.

The renewed fighting comes after the collapse of peace deals under which tribal elders were supposed to take over security in return for a withdrawal of security forces.

The army has suffered scores of casualties this year, many of them in suicide bombings. It is also trying to secure the release of more than 200 soldiers seized in the South Waziristan region at the end of August.

Musharraf has called for moderate political forces to join forces after parliamentary elections due by January to defeat spreading extremism.

He has also vowed to quit as army chief before starting a new presidential term, probably in mid-November, meaning much of the responsibility will fall to his successor.

Gen. Ashfaq Kayani, who took over Monday as vice chief of army staff, is to inherit the top job as soon as Musharraf vacates it.