In an account disputed by Pakistan's army, the US military reported that assailants fired a rocket-propelled grenade at a US CH-47 Chinook helicopter around 0815 GMT on Tuesday as it flew over Chakothi, near the Line of Control that separates the Pakistani and Indian portions of Kashmir.
Pakistani army spokesman Major-General Shaukat Sultan doubted any such attack took place, noting that road-clearing engineers were blasting a road near where the helicopters were flying.
"The blast was huge enough to kick up dust which the pilot probably misunderstood as rocket fire," he said.
US military spokesman Nick Balice said relief flights had restarted on Wednesday after a delay of a couple of hours because of poor visibility.
Balice said US helicopters would stay "a safe distance from the affected area" where the reported attack happened on Tuesday.
At least one Kashmiri group has
vowed not to attack relief teams
Some 24 US military helicopters, mostly heavy-lifting Chinooks diverted from fighting Operation Enduring Freedom in neighbouring Afghanistan, are helping Pakistan recover from the 8 October quake, which is believed to have killed about 80,000 people and left millions homeless and desperately needing supplies before the harsh Himalayan winter closes in.
While Pakistan denies that fighters use its territory as a base, their presence is barely hidden. Fighters have been openly helping with the quake relief effort on both sides of Kashmir.
A spokesman for one prominent group, Jaish-e-Mohammed - which is alleged to have links to al-Qaida and claimed responsibility for a car bombing that killed at least four people in Indian Kashmir on Wednesday - said it would not contemplate attacking any foreigners, including Americans, who are helping survivors of quake.
"All those foreigners, including Americans, who are helping our people in the quake-hit areas are our honourable guests," spokesman Sahrai Baba told the AP, adding, "We cannot even think of doing anything against them".