The Pakistani government ordered security forces to block oil tankers and trucks carrying NATO supplies into Afghanistan at a crucial border crossing Thursday, officials tell CBS News.
All NATO traffic was halted at the Torkham border checkpoint after threats by Pakistani officials to stop providing protection to NATO convoys if the military alliance's choppers hit Pakistani targets again.
Earlier Thursday, Pakistani officials alleged a NATO airstrike hit a border post, killing three Pakistani troops.
"This is the second such incursion of this kind in less than a week. It marks a serious violation of a red line already put in place by Pakistan. We cannot tolerate this kind of behavior," a Foreign Ministry official in Islamabad told CBS News' Farhan Bokhari.
A Pakistani security official based in the northern city of Peshawar told Bokhari that verbal orders had been passed down to authorities at the Torkham crossing to halt traffic.
The official said NATO supply vehicles were being stopped due to "rapidly growing insecurity, which makes it unsafe for us to let the trucks drive on."
"But we all know the reality," the official added.
By midmorning, a line of around 100 NATO vehicles was waiting to cross the border into Afghanistan, officials said.
"We will have to see whether we are allies or enemies," Pakistani Interior Minister Rehman Malik said of the border incident, without mentioning the blockade.
The officials spoke on condition of anonymity because they were not authorized to release the information to the media.
Western military officials in Afghanistan would not comment on the Torkham closure when asked Thursday by CBS News, nor they would give any statistics on the supply route. However, an Afghan Army officer who works closely with NATO forces tells CBS News' Fazul Rahim that at least 70 percent of supplies for U.S. troops and their allies come through Pakistan, and more than half of that amount passes through the Torkham crossing.
A NATO official in Afghanistan confirmed there was an attack in the border area close to the Upper Orakzai region on Thursday, but gave no further details saying the incident was being investigated. He and the Pakistani security officers declined to give their names, citing the sensitivity of the alleged helicopter attack.
The attack was bound to worsen ties between Pakistan and NATO-led forces in Afghanistan at a crucial time in the 9-year war. The supply routes from Pakistan are vital for U.S. and NATO forces operating in Afghanistan, and convoys are often attacked by militants as the cross the border.
Bokhari points out that the orders to halt traffic are still just "verbal," but if Pakistan's government decides to officially halt the flow of supplies into Afghanistan, it would represent a massive logistical challenge for U.S. and NATO commanders, and an equally large diplomatic challenge for Western leaders dealing with an increasingly frustrated Pakistani government.
A European NATO official in Islamabad told Bokhari Thursday that tensions between Pakistan, the U.S. and other NATO nations seem to be rising rapidly.
"For the Western world, Pakistan seems to have become a rapidly growing staging point for militants who attack our troops in Afghanistan. We say Pakistan could do more (to restrain the militants), but hasn't taken adequate steps," said the NATO official, who also spoke on condition of anonymity.
Ahead of the closure, CIA Director Leon Panetta arrived in Islamabad on Wednesday for a two-day visit to meet with key Pakistani leaders.
Pakistan's state-owned television network PTV showed Panetta meeting Prime Minister Yusuf Raza Gilani and other senior officials, including the head of the Pakistan's main intelligence agency, the ISI. PTV's report did not discuss the subject matter of the officials' conversations.
Panetta's visit comes after a record rise in the number of U.S. drone missile strikes on Pakistani soil -- largely believed to be the work of his agency. In September alone, at least 21 strikes have targeted suspected al Qaeda or Taliban sites in the country's lawless border region.
The DAWN newspaper reported that Panetta was seeking a "clear timetable" from Pakistan to launch a new military operation in the North Waziristan region, a volatile area along the Afghan border. The area has long been eyed by U.S. officials as a refuge for militants who routinely attack Western troops in Afghanistan.
Western intelligence officials, all speaking on condition of anonymity, suggested Thursday that some of the recent missile strikes had specifically targeted militant leaders.
Officials said Wednesday the threat was "still active," with some unnamed law enforcement agents even telling CNN that Osama bin Laden himself had signed off on the plans, which allegedly involved teams of well-armed militants simultaneously attacking sites in London, France and Germany.
However, not one of those European governments raised the terror threat level in their countries over the alleged plot, and the officials qualified their warnings by saying there had been no "imminent threat". The posturing led many experts and analysts - including a CBS News source in London with direct access to senior law enforcement agents, to speculate that the news of the plot was little more than a fabrication to justify the fierce bombing in Pakistan.
Relations have been tense since NATO helicopters last weekend opened fire on targets on the Pakistani side of the border, killing several alleged insurgents. Those incidents were protested by Pakistan's government.
Pakistani officials differed on the exact location of the incident, saying it either took place in Upper Kurram or Upper Orakzai. The remote districts neighbor each other and there is no marked border between the two.
The dead men were from a paramilitary force tasked with safeguarding the border, they said. Their bodies had been taken to the region's largest town of Parachinar, said one of them.
Pakistan has a complicated alliance with the United States and NATO that is often subject to tensions.
Pakistan has to balance its support for Western forces in Afghanistan with the intense anti-U.S. feelings of much of its population. Opinion polls show many people regard the United States as an enemy, and conspiracy theories stating U.S. troops are poised to attack Pakistan and take over its nuclear weapons are common.