WASHINGTON: President Barack Obama sees the deaths of 24 Pakistani soldiers in a Nato raid as a tragedy, the White House said Monday, but argued that crisis-wracked US-Pakistani ties were vital to both sides.

White House spokesman Jay Carney said Obama believed Saturday's attack which threw US-Pakistani ties into turmoil was “a tragedy,” adding that “we mourn those brave Pakistani service members that lost their lives.” “We take this matter very seriously,” said Carney, adding that two inquiries by the International Security Assistance Force (ISAF) in Afghanistan and US Central Command would examine what took place.

“As for our relationship with Pakistan, it continues to be an important cooperative relationship that is also very complicated,” Carney said.

“It is very much in America's national security interest to maintain a cooperative relationship with Pakistan because we have shared interests in the fight against terrorism,” Carney said.

Pakistan earlier vowed no more “business as usual” with the United States but stopped short of threatening to break the troubled alliance altogether.

Nato and the United States are trying to limit fallout from the attack but Islamabad has shut vital supply routes to the 140,000 foreign troops serving in Afghanistan.

Pakistan called the strike “unprovoked,” worsening US-Pakistani relations which were already in crisis after the killing in May of Osama bin Laden north of Islamabad by US special forces.

The Wall Street Journal, following a similar report by Britain's Guardian newspaper, cited three Afghan officials and one Western official as saying the air raid was called in to shield allied forces targeting Taliban fighters.

Nato and Afghan forces “were fired on from a Pakistani army base,” the unnamed Western official told the Journal. “It was a defensive action.” An Afghan official said the Kabul government believes the fire came from the Pakistani military base -- and not from insurgents. Afghan-Pakistani relations suffer from routine mutual recriminations.