Tension in Pakistan's north-west has increased in recent months
Pakistan has condemned an alleged raid by foreign troops based in Afghanistan which officials say killed at least 15 villagers in a north-west tribal area.
The South Waziristan raid would be the first ever ground assault into Pakistan by foreign forces from Afghanistan.
Pakistan says the raid was a violation of its sovereignty. On Thursday a US missile killed at least five people in nearby North Waziristan, officials say.
US-led and Nato forces have said they have no reports of any troop incursion.
But off the record, US military sources confirm that US commandoes carried out Wednesday's raid against a suspected al-Qaeda target - and say it could signal a tougher approach to cross-border militancy.
Thursday's attack occurred in the village of Mohammad Khel near Miranshah in North Waziristan, local officials said.
A witness told Reuters news agency that a pilotless US drone had fired at least three missiles at a house where militants were hiding.
'No high-value target'
Pakistani military and political officials say ground troops brought in by US-led coalition helicopters launched the attack in South Waziristan near the Afghan border early on Wednesday morning.
It is not clear who the target might have been.
Locals in the Musa Nikeh area say soldiers attacked with gunfire and bombs. Women and children were among those reported killed. Some officials say as many as 20 people died.
"There is no high-value target or known terrorist among the dead," Foreign Minister Shah Memood Qureshi told the National Assembly on Thursday.
"Only innocent civilians, including women and children, have been targeted."
He said the attack "constitutes a serious escalation in the series of actions" by Nato and US-led forces on Pakistani territory.
Late on Wednesday US Ambassador Anne Paterson was summoned to hear a "very strong protest" at the Foreign Ministry, spokesman Mohammad Sadiq said.
"The ambassador said that she would convey it to her government."
The army called the attack an act of aggression which undermined the fight against militancy.
Correspondents say the army fears such attacks could unite tribesman behind the Taliban.
Prime Minister Yousuf Raza Gilani has said Pakistan will not allow any foreign power to carry out attacks on its territory, inciting a wider uprising in the border area.
He was speaking hours after his motorcade was hit by sniper fire near the capital, Islamabad, on Wednesday. Senior government officials say he was not in the car at the time.
The BBC's Syed Shoaib Hasan in Islamabad says US aircraft have carried out air strikes in the region, but a ground assault would be unprecedented.
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.