Nato helicopters kill 'dozens of rebels' in Pakistan
Nato-led forces say they have killed more than 50 insurgents on Pakistani soil after rare pursuits across the border from Afghanistan.
Apache helicopters are said to have taken part in the operations at the weekend.
They followed an attack by insurgents on an Afghan security outpost in the eastern province of Khost.
Isaf said no civilians were killed in the operation, but this has not been independently confirmed.
Pakistani officials have said the raid was a violation of the country's sovereignty.
In a statement quoted by the Associated Press news agency, Pakistan's Ministry of Foreign Affairs said it would have to "consider response options".
The BBC's Adam Mynott in Islamabad says Nato in Afghanistan has an agreement with the Pakistani authorities for the right of "hot pursuit" over the border.
The raids, however, will do nothing to improve anti-American sentiment which is being fuelled by escalating numbers of drone attacks on targets in Pakistan, our correspondent adds.
In a statement, the International Security Assistance Force (Isaf) in Afghanistan said Afghan forces in Khost had been attacked on Friday by "a significant number of insurgents".
The statement added: "An air team in the area observed the enemy fire, and following International Security Assistance Force rules of engagement, crossed into the area of enemy fire."
Isaf told the BBC its aircraft had killed 49 insurgents.
On Saturday, two Apache helicopters came under small-arms fire from the same area and again crossed the border, killing four to six insurgents, said Isaf.
Pakistani media said fighters from the Haqqani network, a branch of the Afghan Taliban which operates in Pakistan, died in the Nato air raids.
An Isaf spokesman, Sgt Matt Summers, confirmed the helicopters had crossed into Pakistan.
But he did not reveal the location of the operation or say which Isaf country's forces were involved.
Meanwhile, four militants died on Monday in a suspected US drone strike on a house in north-western Pakistan, local security officials said.
The raid took place in Khushali Toorikhel village, south-east of Miranshah, the main town in North Waziristan tribal district.
The region is a stronghold of Taliban and al-Qaeda militants and American forces regularly use drones for missile strikes in the area, but manned air raids across the border are rare.
Isaf's force was established by the UN in late 2001 with a stated mission of promoting security and development; it is also training Afghan soldiers and police.