Pakistani officials say NATO helicopters from Afghanistan have attacked a military checkpoint in northwest Pakistan, killing 25 troops and wounding at least 14 others.

Pakistan retaliated within hours by closing the Torkham border crossing with Afghanistan, suspending NATO supply convoys into the neighboring country.

A Pakistani military spokesman said the pre-dawn attack Saturday in Salala, a village in the restive Mohmand tribal area near the Afghan border, was “unprovoked and indiscriminate.” Authorities say about 40 soldiers were stationed at the post.

NATO officials say they are aware of the incident and are investigating.

Top NATO and U.S. commander in Afghanistan General John Allen has offered his condolences to families and loved ones of any members of the Pakistani security forces who may have died or were wounded.

Prime Minister Yousef Raza Gilani has ordered the Foreign Ministry to take up the matter in “the strongest terms” with NATO and the U.S.

U.S. officials have said Pakistan's tribal belt provides sanctuary to the Taliban, which has been fighting for 10 years against U.S. troops in Afghanistan.

The helicopter raid comes a little over a year after a similar, less deadly operation in which U.S. helicopters killed two Pakistani soldiers near the Afghan border who were mistaken for insurgents. Pakistan responded to that attack as it did Saturday – by closing down the Torkham border crossing to NATO supplies. It was closed for more than a week, until the U.S. apologized.

Ties between the U.S. and Pakistan have been unraveling since a covert U.S. commando raid that killed al-Qaida leader Osama bin Laden in a Pakistani garrison town on May 2. Pakistan was outraged it was not informed beforehand and angered by what it saw as a U.S. violation of Pakistan's sovereignty.