Pakistan is supposed to be an important and trusted ally fighting a common enemy, but for a brief time today, U.S. and Pakistani troops exchanged fire in an incident that began with Pakistani forces firing at two U.S. helicopters they claim had entered Pakistani airspace.
There are no reports of any injuries.
Senior U.S. officials say it all started as U.S. helicopters were providing cover for U.S. and Afghan troops patrolling along the Pakistan border in Afghanistan's Khowst province.
The helicopters came under fire from Pakistani soldiers at a border checkpoint. As the helicopters retreated, U.S. officials told ABC News, U.S. ground troops fired warning shots in the direction of the border checkpoint. The Pakistanis shot back, prompting a firefight between the two sides that lasted about five minutes.
Pakistani officials say the American helicopters were flying in Pakistani airspace; U.S. officials insist they were more than a mile inside Afghanistan.
"The flight path of the helicopters at no point took them over Pakistan," Pentagon spokesman Bryan Whitman said.
A senior U.S. military official told ABC News, "They were very certain they were in Afghanistan," noting that, with GPS tracking systems, the helicopter pilots were able to identify their location with certainty.
The Pakistani military released a statement confirming that its forces fired "anticipatory warning shots" at two helicopters they claim had passed over a border post and were "well within Pakistani territory."
The statement also claimed that "the helicopters returned fire and flew back" into Afghanistan.
There is also disagreement on what precisely the Pakistani troops fired at the helicopters. U.S. military officials say it was gunfire, but speaking to reporters at the U.N., Pakistani President Asif Ali Zardari said the Pakistani troops simply fired flares.
"They are flares just to make sure that they know they have crossed the borderline," Zardari said. "Sometimes the border is so mixed that they don't realize that they crossed the border."
Also at the U.N. today, U.S. Secretary of State Condoleezza Rice agreed that the border between Pakistan and Afghanistan is "very, very unclear," and "one of the most inhospitable places."
This comes at a tense time for U.S.-Pakistani relations. In recent weeks, the U.S. has quietly stepped up secret military operations against militants inside Pakistan. Those attacks have prompted loud protests from the Pakistani people and their government.
Still, U.S. officials continue to insist Pakistan is a steadfast ally -- even one of America's most important allies -- in the fight against terrorism.