Pakistan orders U.S. to shut major down air base

America's already troubled relationship with Pakistan is under new strain on Saturday. Pakistan is accusing NATO helicopters of killing at least 25 Pakistani soldiers in an attack on army outposts along the border with Afghanistan. In response, Pakistan has ordered the U.S. to shut down a major air base. CBS News correspondent Whit Johnson is in Washington Saturday with more.

As coalition forces battled insurgents along the poorly defined Afghanistan/Pakistan border, NATO aircraft hit two Pakistani outposts.

"Close air support was called in, in the development of the tactical situation, and it is what highly likely caused the Pakistan casualties," said ISAF spokesman Gen. Carsten Jacobson, who immediately promised an investigation.

"We don't know numbers," he said, "we don't know the magnitude of the incident..."

Anti-NATO tension builds in Pakistan
NATO: "Highly likely" it killed Pakistanis

Pakistan's Prime Minister Gilani condemned what he called an attack on the nation's sovereignty. In the first ultimatum of its kind, his government gave the United States 15 days to vacate Shamsi air base, the unofficial hub for U.S. drone strikes in Pakistan.

The country also sealed off crucial overland supply routes, which in recent months accounted for 30 percent of all cargo bound for U.S. forces in Afghanistan.

"It is like putting a finger at the jugular vein of a human being, literally in terms of the war machine," according to Akbar Ahmed, chair of Islamic studies at American University. He said the killing of Pakistani soldiers risks angering the nation as much as the bin Laden raid -- a surprise attack on Pakistani soil.

On the flip side, the U.S. blames Pakistan for harboring militants that kill coalition forces and even attacked the U.S. embassy in Kabul.

"Is this a deal breaker for the relationship between the U.S. and Pakistan?" asked Johnson to Akbar.

"I don't think so. I think Pakistan, certainly the establishment, including the military establishment, understand the importance of a close alliance with the United States."

Late Saturday, the White House extended condolences for the loss of life. Military experts told CBS News that evicting the U.S. from Shamsi air base will have some operational impact, but drones can be and are launched from elsewhere including Afghanistan. The closure of supply routes, however, is likely more damaging as cargo and fuel trucks back up at the border.