MIRANSHAH, Pakistan, July 22 (Reuters) - Pakistan's army has killed up to 13 pro-Taliban fighters in North Waziristan, the military said on Sunday, amid escalating violence in the troubled region after militants tore up a peace pact with the government.

Armed militants, in small groups, attempted to attack several army posts on Saturday night but their bid was foiled.

"Our forces were alert. They retaliated and killed up to 13 militants," military spokesman Major-General Waheed Arshad told Reuters.

The soldiers suffered no losses, he added.

The militants riding in three to four vehicles opened fire at the army post in Ghulam Khan area, near the Afghan border, on Saturday evening.

The soldiers returned the fire, killing up to four militants.

The militants later attacked a complex of posts in the same region but soldiers thwarted their attempt and killed nine of them.

Arshad said seven militants were also arrested.

Separately, four soldiers were wounded when their convoy was hit by a roadside bomb, prompting a shootout.

Arshad said there had been few casualties on militant side.

Residents said army helicopter gunships also fired at militant hideouts during the fighting.

Arshad said gunships were carrying out surveillance of the area. "If needed they can be used."

Pakistan's Waziristan region has long been regarded as a safe haven for al Qaeda and Taliban militants sheltered by their local Pashtun allies.

Pakistani authorities struck a deal with the local militants last September in a bid to isolate foreign militants and curb their cross-border incursions into Afghanistan.

But the militants scrapped the deal last week, adding to a concern over a deteriorating security situation in the volatile region.

AL QAEDA GAINING STRENGTH

U.S. President George W. Bush said on Saturday he was troubled by a U.S. intelligence report that al Qaeda was gaining strength in the Pakistani tribal region.

In his taped weekly radio address, Bush said Pakistani tribal leaders had proven unwilling or unable to police the area themselves.

However, he said ally Pakistan was committed to fighting militants. "President Pervez Musharraf recognises the agreement has not been successful or well-enforced and is taking active steps to correct."

The U.S. report made public this week found a "persistent and evolving" threat to the United States from Islamic militant groups, especially Osama bin Laden's al Qaeda.

U.S. officials have said the United States never ruled out any options when it came to striking against al Qaeda or the Taliban.

Pakistan rejected the statements as "irresponsible and dangerous" and said only its own troops could carry out counter-terrorism actions on its soil.

The militants have launched several attacks and ambushes in North Waziristan since the scrapping of the peace deal.

They were also enraged over the storming of a radical mosque in the capital, Islamabad, this month by army commandos, and have carried out a series of bomb and suicide attacks across the country to avenge the assault.