Pakistan has said NATO-led raids that crossed over its border from Afghanistan at the weekend violated a UN mandate. Security forces said more than 50 insurgents were killed.
The International Security Assistance Force (Isaf) said it had crossed over the border into Pakistan after coming under fire in the Khost region of Afghanistan. It said 49 insurgents had been killed, the BBC reports.
Two Apache helicopters again crossed the border on Saturday, killing four to six insurgents, after coming under small-arms fire from the same area, it said.
Isaf says no civilians were killed in the operation - but that has not been independently confirmed.
It has said the raids followed its rules of engagement in the region and that it has the right to enter Pakistan's airspace while pursuing a target.
But in a statement, Pakistan's ministry of foreign affairs said the incidents had been "a clear violation and breach of the UN mandate under which Isaf operates".
It said Isaf's mandate ended at the Afghan border and there were "no agreed 'hot pursuit' rules" allowing Isaf troops to cross into Pakistan.
Pakistani media say that Isaf helicopters hit a group of fighters from the Haqqani network, a branch of the Afghan Taliban which operates in Pakistan.
Only US uses Apaches
An Isaf spokesman confirmed that the helicopters had crossed into Pakistan but did not reveal the location of the operation or say which countries' forces were involved.
Analysts say the only coalition member using Apache helicopters in Afghanistan is the US.
American forces regularly use drone aircraft for missile strikes in Pakistan's tribal belt, 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.