Pakistani troops have fired at two US helicopters forcing them back into Afghanistan, local Pakistani intelligence officials say.
The helicopters flew into the tribal North Waziristan region from Afghanistan's Khost province at around midnight, the reports say.
Tensions have risen after an increase in US attacks targeting militants.
The incident comes amid mounting security fears after a militant bomb attack on the Islamabad Marriott hotel.
Pakistan's army has said it will defend the country's sovereignty and reserves the right to retaliate to any border violations.
The government has said it will take targeted action against the militants, promising raids in some "hotspots" near the border with Afghanistan.
Meanwhile in the city of Peshawar, Afghan consul Abdul Khaliq Farahi was kidnapped after six unidentified men ambushed his car, officials say. His driver died in the attack.
'Firing in the air'
Last week Pakistani troops fired into the air to prevent US ground troops crossing the border into South Waziristan.
The latest confrontation between US and Pakistani forces took place in North Waziristan's sparsely populated Ghulam Khan district, west of the main town in the region, Miranshah, local officials say
