Military officials in Pakistan say thousands of troops are engaged in heavy fighting with suspected foreign militants for a third day in a tribal region bordering Afghanistan. Some 50 people have been killed in the fighting so far.

The clashes are taking place in the semi-autonomous tribal region, known as South Waziristan.

The area borders Afghanistan, and Pakistani authorities believe scores of foreign militants and al-Qaida terrorists have bases there.

Witnesses say Pakistani ground troops backed by helicopter gunships are pounding a small mountainous village in the area, called Shakai.

Military spokesman Major-General Shaukat Sultan says both sides have suffered casualties since the fighting began Wednesday.

"The present activity is going on in area Shakai where there are confirmed hideouts of the miscreants," he said. "Over 35 miscreants have been killed and the security forces have also lost 15 personnel."

Since March, the government has tried and failed to persuade rebel tribesmen to surrender foreign al-Qaida suspects living among them. Earlier this month, Pakistani authorities imposed economic sanctions on the tribe allegedly sheltering the Islamic militants, but that tactic failed to produce results.

Jamshed Ayaz Khan is a former military general and head of the government-funded Institute of Regional Studies in Islamabad. He says the Pakistani government has tried a number of tactics, and until now has been patient in its dealings with the tribal leaders.

"Pakistan government tried everything possible to solve the Wana problem politically? So finally then came on the economic blockade and then now on going towards a military operation," he said.

In a major military operation in the tribal region earlier this year, more than 100 people, including 48 government soldiers, were killed.

On Thursday, a top army general escaped an assassination attempt in the southern Pakistani city of Karachi. Senior government officials say they are looking into the possibility that the attack was motivated by revenge, and carried out by supporters of militants being hunted in the tribal regions. Ten people, mostly soldiers, were killed in the attack, but the general escaped unhurt.