SHALTALO, PAKISTAN . The Pakistani Taliban claimed responsibility on Friday for a cross-border attack on a security checkpost that appeared to signal that the group was adopting a new strategy of carrying out largescale attacks on government and army targets.

In the pre-dawn raid Wednesday in the village of Shaltalo in the Dir region, up to 400 terrorists crossed over from Afghanistan in the raid, which triggered more than 24 hours of clashes, the government said.

Twenty-seven Pakistani forces were killed and 45 insurgents died in the clashes in the northwest, security officials said. There were contradictory accounts of casualties and how many terrorists fought.

"Up to 40 to 50 of our fighters took part in the operation," Ehsanullah Ashen, spokesman for the TehrikeTaliban Pakistan (Taliban Movement of Pakistan), told Reuters by telephone from an undisclosed location. "None of our fighters were killed."

The TTP has previously brought fighters from across the porous border with Afghanistan -where it has allies -to attack Pakistani security forces, but none was on the same scale as the Dir operation.

Deputy TTP leader Fakir Mohammed said the group with close ties to al-Qaeda had changed strategy and would now focus on large-scale attacks only on state targets like the one in Dir. "Our new strategy of launching big attacks on military installations was aimed at causing demoralization in the ranks of the security forces and tiring of the government," he told Pakistan's The News newspaper from what he said was a location somewhere in Afghanistan.

A new TTP plan may complicate the army's efforts to weaken the group, which has stepped up suicide bombings to avenge the killing of Osama bin Laden by U.S. special forces in a Pakistani town on May 2.

Since then, the movement has attacked paramilitary cadets, a naval base, a U.S. consulate convoy and other targets, challenging government assertions that army offensives against terrorists have succeeded.

After bin Laden's death, the United States reiterated its call for Pakistan to crack down harder on insurgents, especially those who cross over to Afghanistan to attack Western forces.

The lawless frontier is home to some of the world's most dangerous groups, who are intricately linked and cross back and forth across fairly easily to carry out operations.

Pakistan's army will have to contend with a new TTP strategy at a time when it is still reeling from the bin Laden fiasco.

The U.S. raid opened the agency up to international suspicion it was complicity in hiding the al-Qaeda leader, and to domestic criticism for failing to detect or stop the U.S. team.

Pakistan, dependent on billions of dollars in aid from its strategic ally Washington, is under more pressure than ever to tackle militancy because of the discovery bin Laden was living close to Islamabad. As the Dir operation showed, it won't be easy.