ISLAMABAD, Pakistan — Pakistan on Saturday blocked vital supply routes for U.S.-led troops in Afghanistan and demanded Washington vacate a base used by American drones after coalition aircraft allegedly killed 24 Pakistani troops at two posts along a mountainous frontier that serves as a haven for militants.
Pakistani authorities said Saturday's assault was unprovoked and denounced it as a gross violation of their country's sovereignty. Army Chief of Staff Gen. Ashfaq Parvez Kayani condemned the attack as "a blatant and unacceptable act."
The strikes, which Pakistani officials said involved both helicopters and fighter jets, took place Saturday around 2 a.m. at two military posts in Pakistan's Mohmand tribal region that borders Afghanistan's Kunar province.
At least 40 soldiers were deployed at the posts, which Pakistani officials said were established to repulse cross-border attacks by Afghan militants and the Taliban. NATO aircraft penetrated roughly a mile and a half into Pakistan to make the strikes and, in addition to the dead, at least 13 soldiers were injured, according to Pakistani officials.
The Obama administration pledged to conduct a full investigation into the attack. Secretary of State Hillary Rodham Clinton and Defense Secretary Leon Panetta in a joint statement said they had each spoken to their Pakistani counterparts to express their condolences for the loss of life.
A statement from the White House also offered condolences but did not address Pakistan's decision to block supply routes for the war in Afghanistan or its demand that the United States vacate the drone base.
NATO spokesman Brig. Gen. Carsten Jacobson told the BBC it was "highly likely" that alliance aircraft caused the deaths. He said close air support was called in when "a tactical situation developed on the ground," but gave no further details.
The U.S. ambassador in Islamabad, Cameron Munter, called an emergency meeting and expressed regret over the Pakistani casualties. And Gen. John Allen, the commander of NATO-led forces in Afghanistan, offered condolences to families of the dead and promised an investigation.
"This incident has my highest personal attention and my commitment to thoroughly investigate it to determine the facts," he said in a statement.
The airstrike came a day after Allen met with Kayani to discuss border coordination and control.
If confirmed, it would be the deadliest friendly-fire incident by NATO against Pakistani troops since the Afghan war began a decade ago.
After an emergency meeting of the Cabinet's defense committee chaired by Pakistani Prime Minister Yousuf Raza Gilani, the government said it had closed both its border crossings to NATO.
It also said that within 15 days the United States must vacate Shamsi air base, which is located in southwestern Baluchistan province. The Pakistani government also plans to review all diplomatic, military and intelligence cooperation with the United States and other NATO forces, according to the statement.
Shamsi was used to launch the war in Afghanistan in late 2001, then later served as the base for the U.S. drone program targeting militants, according to McClatchy Newspapers.
A prolonged closure of Pakistan's Afghan border crossings to NATO supplies could cause serious problems. The United States, which is the largest member of the NATO force in Afghanistan, ships more than 30 percent of its nonlethal supplies through Pakistan. The coalition has alternative routes through Central Asia into northern Afghanistan, which are costlier and less efficient.
Pakistan closed one of its Afghan crossings to NATO supplies for 10 days last year after U.S. helicopters accidentally killed two Pakistani soldiers. Suspected militants took advantage of the impasse to launch attacks against stranded or rerouted trucks carrying NATO supplies. The government reopened the border when the United States apologized.
But the reported casualties are much greater this time, and the relationship between Pakistan and the United States has severely deteriorated over the past year, especially following the covert American raid that killed Osama bin Laden in a Pakistani garrison town in May. Islamabad was outraged it wasn't told about the operation beforehand.
Information from the Associated Press, Los Angeles Times and New York Times was used in this report.