Pakistan demanded evidence Saturday for Indian charges it was involved in the Mumbai attacks and reversed its decision to send its spy chief to aid the probe, muddying efforts to avert a crisis between the nuclear-armed neighbors.

Deep mistrust between the South Asian rivals, who have already fought three wars, endangers efforts by the U.S. and its Western allies to battle Al Qaeda and Taliban, thought to be hiding out along Pakistan's western border with Afghanistan.

Rising tensions on Saturday prompted Pakistani security officials to warn that the government would pull its troops from the antiterror fight along the Afghan border in order to respond to any Indian mobilization.

But Washington, which is fighting an increasingly deadly insurgency in Afghanistan, issued a reminder of Pakistan's failure to eliminate militant strongholds in its lawless northwest with a missile attack that reportedly killed two people.

Pakistan's government on Saturday reinforced its pledge to help India identify and apprehend those behind the attacks, which left more than 190 people dead in the financial hub of Mumbai.

"We stand shoulder to shoulder with the Indian people to defeat this common enemy," Foreign Minister Shah Mehmood Qureshi told a news conference in Islamabad.

However, Qureshi insisted that Pakistani authorities — including intelligence agencies that New Delhi has long accused of sponsoring terrorism — were not behind the carnage.

"If they have evidence they should share it with us," Qureshi said. "Our hands are clean."

His government also backed off a pledge made on Friday to send the chief of its Inter Services Intelligence agency in person.

Pakistani President Asif Ali Zardari blamed the about-face on a "miscommunication" with India. Zardari said Prime Minister Manmohan Singh had asked in a telephone call on Friday only that a "director" of the agency — not the chief — go to India.

But the reversal followed sharp criticism from some Pakistani opposition politicians and a cold response from the army, which controls the agency and jockeys with India for influence in the region.

Two senior Pakistani security officials said the Indians were pointing fingers at Islamabad in order to divert attention from its failure to avert the attacks and radicalization among its own Muslim minority.

One of the officials, both of whom spoke on condition of anonymity because of the sensitivity of the situation, said a further ratcheting up of tension could prompt India to move forces toward the Pakistani border.

Asked how Pakistan would respond, the second official said it would pull all its troops from the hotspots along the border with Afghanistan to its already highly militarized eastern frontier.

"All troops from our western border would be withdrawn to redeploy them at the eastern border," the official said. "Not a single soldier will remain there, and the coalition partners know about it."

He acknowledged that there was no indication of India mobilizing its forces. However, he claimed that India's air force has been put on "red alert."

Indian Air Force spokesman Sq. Ld. Mahesh Upasani declined to comment.

Hassan Abbas, a Pakistan expert at Harvard University's Kennedy School of Government, said the army was probably riled by Indian and U.S. media reports suggesting that New Delhi was considering a military response, including air strikes on suspected militant training camps in the portion of Kashmir controlled by Pakistan.

Indian saber-rattling was inevitable as parties pander to nationalist sentiment ahead of general elections due next year, Abbas said, though he estimated the risk of war as slim.

India has repeatedly accused Pakistan of complicity in terrorist attacks traced to groups fighting in Kashmir.

Pakistan insists its support for agitation in Kashmir, where anti-India sentiment runs high, is only moral and political. But it is widely believed to have supported rebels with training and equipment.

Infiltration into Kashmir from Pakistan has eased in recent years under U.S. pressure, and relations have improved under a peace process begun in 2004.

But ties nose-dived again in July when India accused Pakistan's spy agency of involvement in the bombing of its embassy in the Afghan capital, Kabul.

President-elect Barack Obama has identified rapprochement between the two countries as a main plank of his plan to stabilize Afghanistan and defeat al-Qaida.

Still, a clear Pakistani link to the attacks could also support Washington's goals if it persuades Islamabad to take tougher action against militants on its soil.

U.S. forces have increasingly taken matters into their own hands by launching more than 20 suspected missile strikes in Pakistan since August, despite protests that the tactic is fueling hard-line Islamist sentiment.

Two Pakistani intelligence officials said Saturday's strike destroyed a house in the North Waziristan region. The officials, speaking on condition of anonymity because of the sensitivity of their work, said several more people were injured. The identity of the victims was not clear.