Islamabad - As Taliban activities rise to a disturbing level in Afghanistan, the relations between two close allies in the war on terror - United States and Pakistan - seem to be souring.

Hours after Wednesday's statement by the Chairman of the US Joint Chiefs of Staff, Admiral Mike Mullen, that Washington was planning military operations to eliminate militant sanctuaries in Pakistan, Pakistan's army chief vowed to defend sovereignty and territorial integrity of the country "at all cost."

The top US military official told the Congress' Armed Services Committee that the armed forces were not winning the war against the Taliban in Afghanistan and a "new, comprehensive strategy," involving Pakistan's tribal belt from where the rebels launch cross-border attacks on coalition forces, was needed.

Apparently the revised policy has already been put to work.

A report in New York Times on Thursday said President George W Bush had in July secretly approved orders for ground assaults inside Pakistan without the prior consent of Islamabad.

"The situation in the tribal areas is not tolerable," a senior American official, who spoke on condition of anonymity, told the newspaper. "We have to be more assertive. Orders have been issued."

This allowed US special forces, backed by helicopter gunships, to raid a border village in the tribal district of South Waziristan, killing more than 20 people, mostly civilians, Pakistani officials said. It evoked anger in Pakistan where demands are mounting to end the cooperation with the US against terrorism.

"Such reckless actions only help the militants and further fuel the militancy in the area," Pakistan's military chief Ashfaq Parvez Kayani said. "No external force is allowed to conduct operations inside Pakistan."

Coalition forces have largely relied on Pakistan to quell Taliban and al-Qaeda-led militancy in its border areas since they invaded Afghanistan in 2001.

Yet, with currently more than 120,000 Pakistani troops along the frontier, rebel cross-border raids continue, giving rise to suspicions in Washington that some rouge elements within the Pakistan Army and the powerful intelligence agencies are supporting the insurgency.

Candidates in the US election campaign increasingly call for a focus on Pakistan to effectively counter Afghanistan's Taliban, where attacks on coalition forces have increased by 40 per cent this year.

Democratic hopeful Barack Obama said Wednesday: "The central front is in Afghanistan and Pakistan, where the terrorists who hit us on 9/11 are still plotting attacks seven years later."

However, General Kayani urged "strategic patience. There are no quick fixes in this war. Falling for short term gains while ignoring our long term interest is not the right way forward," he warned.

Pakistan has long been advocating a "multi-pronged" strategy to tackle insurgency. But the policy remains limited to mere diplomatic jargon and failed whenever put into practice.

The new government, which is led by the liberal Pakistan People's Party of slain former prime minister Benazir Bhutto, launched indirect peace talks with the Islamist insurgents after it took over in March. But they broke down before the sides could agree on anything.

"Pakistan's indecision on how to deal with militancy and clear-cut disagreement over US attacks on its soil has strained the relations between Washington and Islamabad," said Hasan Askari Rizvi, a leading Pakistani political scientist and visiting scholar at the John Hopkins School of Advanced International Studies in Washington.

Americans do not want to put Pakistan's nascent government in a difficult position by regularly conducting cross-border strikes, but "the US administration realizes that to win the war in Afghanistan action has to be taken in Pakistan's tribal areas," Rizvi added.