WASHINGTON, Oct. 1 (Xinhua) -- U.S. Defense Department on Friday said U.S. and NATO operations in Afghanistan haven't been affected by Pakistan's closure of a major supply route a day before.

The closure of the crossing at Torkham Gate along the border of Afghanistan and northwestern Pakistan came after U.S. helicopters "unknowingly killed several Pakistani border guards," said Dave Lapan, a Pentagon spokesman.

"It is still the case, at last reports, that Torkham Gate remains closed," Lapan said. "We are still discussing with the Pakistan government that Pakistanis resolve this and get it re- opened, but in the meantime, there is still no immediate impact on our operations in Afghanistan."

About 50 percent of coalition forces' non-lethal supplies, such as water, food and fuel come into Afghanistan from Pakistan's Torkham and Shaman gates, he said.

The incident was not the first such attack this week where American aircraft killed Pakistanis that were not insurgents. Lapan said rising tensions among Pakistanis along the border prompted Pakistan's decision to close the gate.

"What the Pakistani military described to us was that the closure of the gate was due to their concerns over rising tensions, " he said. "It was to them a security issue; tensions in the area due to these incidents."

Such tensions led to a militant attack on a NATO convoy this morning in southern Afghanistan. The convoy was carrying fuel, traveling about 250 miles north of Karachi when militants torched more than two dozen trucks. Pakistani officials are investigating that attack.