The Pakistani army and the Taliban claimed to be inflicting heavy casualties on each other as fierce fighting raged Sunday on the second day of a military assault on an Al Qaeda and Taliban sanctuary close to the Afghan border.

The outcome of the operation in South Waziristan stands to shape the future of nuclear-armed Pakistan and the militant groups seeking to topple its U.S.-backed government. The region is home to jihadists behind soaring terrorist attacks around the country, as well as Al Qaeda and other extremists believed to be plotting strikes in the West.

The army said 60 militants had been killed on the first day of the operation, while six soldiers had died. The Taliban claimed to have inflicted "heavy casualties" on the army and to have pushed invading soldiers back into their bases.

It was not possible to independently verify the conflicting claims because the army is blocking access to the battlefield and surrounding towns.

"We know how to fight this war and defeat the enemy with the minimum loss of our men," Taliban spokesman Azam Tariq told The Associated Press from an undisclosed location. "This is a war imposed on us and we will defend our land till our last man and our last drop of our blood. This is a war bound to end in the defeat of the Pakistan army."

Tariq also said the Taliban were behind three commando-style raids on law enforcement agencies in the eastern city of Lahore on Thursday that killed around 30 people as well as the deadly bombing of a police station in the northwestern city of Peshawar a day later.

Accounts from residents and those fleeing South Waziristan on Sunday suggested that the 30,000 Pakistani troops were in for a bloodier time than in the Swat Valley, another northwestern region that the army successfully wrested away from insurgents earlier this year.

"Militants are offering very tough resistance to any movement of troops," Ehsan Mahsud, a resident of Makeen, a town in the region, told The Associated Press in the town of Mir Ali, close to the battle zone. He and a friend arrived there early Sunday after traveling through the night.

Mahsud said the army appeared to be mostly relying on air strikes and artillery against militants occupying high ground. He said the insurgents were firing heavy machine guns at helicopter gunships, forcing the air force to use higher-flying jets.

The army is up against about 10,000 local militants and about 1,500 foreign fighters, most of them from Central Asia. They control roughly 1,275 square miles (3,310 square kilometers) of territory, or about half of South Waziristan, in areas loyal to former militant chief Baitullah Mehsud, who was killed in a U.S. missile strike in August.

Officials have said they envisage the operation will last two months, when winter weather will make fighting difficult.

A brief army statement said 60 militants had been killed, along with six soldiers, since Saturday. It said the army had secured high regions close to Razmak, where the army has had a base for several years, and destroyed six militant anti-aircraft gun positions.

A resident in Wana -- the main town in South Waziristan and in the heart of Taliban-held territory -- said the insurgents had left the town and were stationed on the borders of the region, determined to block any army advance.

"All the Taliban who used to be around here have gone to take their position to protect the Mehsud boundary," Azamatullah Wazir said by phone Sunday. "The army will face difficulty to get in there."

Intelligence officials said Saturday that the ground troops were advancing on two flanks and a northern front of a central part of South Waziristan controlled by the Mehsuds. The areas being surrounded include the insurgent bases of Ladha and Makeen, the officials said on condition of anonymity because they were not allowed to brief the media.

As many as 150,000 civilians -- possibly more -- have left in recent months after the army made clear it was planning an assault, but as many as 350,000 could still be in the region. The United Nations has been stockpiling relief supplies in a town near the region, but authorities are not expecting a major refugee crisis like the one that occurred during the offensive this year in the Swat Valley.

Over the last three months, the Pakistani air force has been bombing targets in South Waziristan, while the army has said it has sealed off many Taliban supply and escape routes. The military has been trying to secure the support of local tribal armies in the fight.