Pakistani Defense Minister Ahmed Mukhtar says aircraft belonging to foreign forces in Afghanistan carried out overnight attacks on three houses in Pakistani territory.
Mukhtar says the operation took place at about 4:30 a.m. local time. He declined to comment further, saying that the incident was being investigated by Pakistan's Foreign Ministry.
Reports say the attack took place in the village of Musa Nika Ziarat near Angor Adda in the tribal region of South Waziristan -- known to be a sanctuary for Al-Qaeda and Taliban militants.
But there are differing accounts of the overnight operation. Some witnesses say it was carried out by helicopter gunships. Others spoke of an attack by ground troops as well -- which, if confirmed, would be the first confirmed raid involving foreign troops in Pakistan and would likely to spark an uproar there.
Gul Nawaz, a shopkeeper in the village, said more than a dozen foreign commandos disembarked from one of the helicopters and raided the three houses. Other residents said foreign troops detained some people and took them away.
However, there was no immediate confirmation from NATO, the United States, or Pakistan about the arrest of Al-Qaeda or Taliban fighters.
Owais Ahmed Ghani, the governor of Pakistan's North West Frontier Province, said he was furious about the raid, calling it "outrageous" and "a direct assault on the sovereignty" of Pakistan.
Ghani said 20 people were killed in the raid -- including women and children. He also said the people of Pakistan expect the country's armed forces to "rise to defend the sovereignty of the country and give a befitting reply."
A spokeswoman for the NATO-led International Security Assistance Force in Afghanistan said she had no information about the attack.
A spokesman for the separate U.S.-led antiterrorism coalition forces in Afghanistan declined to comment.
RFE/RL's Radio Free Afghanistan spoke to an independent Pakistani journalist in the area -- Sailab Masood -- who has been investigating the incident. Masood says that according to his sources, foreign commandos did take part in a ground operation with the support of helicopters.
"The commandos descended from their helicopters and went into the house of a tribesman identified as Paeo Jan Wazir. Inside the house they met resistance," Masood said. "The information we have so far indicates that at least 19 people were killed in this raid and 20 more were injured. The dead included seven women and three children."
U.S.-operated unmanned aircraft reportedly have carried out air strikes several times this year on foreign militants sheltering in Pakistan's border regions, killing dozens of foreign fighters.
Pakistan's military has been engaged in offensive operations against militants in the tribal regions for months. But on September 1, just hours before the latest raid, Islamabad declared a unilateral cease-fire that it said would last through the month of Ramadan.
Pakistan is an ally of the United States in the war against terrorism. But the campaign against militancy is deeply unpopular with many Pakistanis. Islamabad previously has ruled out operations by foreign soldiers on its territory.
Analysts say today's reports of foreign troops on Pakistani soil are likely to spark an uproar in Pakistan, where a new civilian government is struggling to assert its authority and presidential elections are set for September 1.