Tension in Pakistan's north-west has increased in recent months
Foreign troops based in Afghanistan have attacked targets inside north-west Pakistan, killing at least 15 people, witnesses and officials say.
The governor of North West Frontier Province called it an "outrageous" assault on Pakistan's sovereignty.
The attack is said to have involved helicopters in the tribal area of South Waziristan, close to the Afghan border.
US-led and Nato forces said they had no reports of any such incursion. Border tensions have risen in recent weeks.
The BBC's Barbara Plett in Islamabad says the US occasionally launches air strikes against militant targets in Pakistan's border region, sometimes in co-ordination with the Pakistani army.
But a raid by ground troops would be rare. It is not clear who the target of any attack might have been.
In other violence, Pakistani security forces killed up to 30 militants and injured dozens more in the Swat valley north-west of Islamabad, the military says.
Locals say three helicopter gunships dropped international troops in the Musa Nikeh area of South Waziristan, located on the border with Afghanistan, early on Wednesday morning.
They say the soldiers killed more than a dozen people with gunfire and bombs, including women and children.
"Troops came in helicopters and carried out action in three houses," Gul Nawaz, a shopkeeper, told Reuters news agency.
Witnesses told the BBC Urdu service that troops entered the house of a local tribesman, opened fire and then lobbed a bomb in the house.
They said at least nine bodies had been recovered from the debris. The witnesses said the family was not known for links with militants.
North West Frontier Province (NWFP) Governor Owais Ahmed Ghani, who is in administrative charge of the tribal areas, put the death toll higher.
A statement condemned what he called a "cowardly" attack by coalition commandos.
"At least 20 innocent citizens of Pakistan, including women and children, were martyred," it said.
"It is outrageous... This is a direct assault on the sovereignty of Pakistan."
Pakistan's army has confirmed an attack but says it is still investigating the details.
There is mounting US pressure on Pakistan - a key ally in the "war on terror" - to crack down on militants, who use the border region to launch raids into Afghanistan.
The Afghan government and Nato say the border region is a haven for al-Qaeda and the Taleban. Pakistan says it is doing all it can to curb militancy.
On Monday, Pakistan's military suspended its operations against Taleban militants in the neighbouring Bajaur tribal area.
The government said this suspension of fighting was to respect the fasting month of Ramadan.
Taleban spokesman Maulvi Omar welcomed the announcement, but he said militants would not lay down their arms.