“Two helicopters intruded several kilometres inside Pakistan territory in Datta Khel town around 2:00 am (2100 GMT Tuesday),” a military official told AFP, speaking on condition of anonymity.

The helicopters flew in from the eastern Afghan province Paktia and circled the bordering village of Zoi Nara for more than five minutes, the official in the provincial capital Peshawar said.

Another military official said the choppers left after “warning shots” were fired by Pakistan troops.

Officials said they were not attack helicopters.

Dildar Khan, a tribal police official in Datta Khel, said the helicopters flew at a relatively low altitude and returned after the warning shots.

Militants are dug in on both sides of the border and US Secretary of State Hillary Clinton last week called on Pakistan to do more to squeeze militant havens on its territory, particularly those of the Haqqani network.

Nato said on Monday that 200 Taliban-linked militants were killed or captured in military operations along the border designed to hit the insurgency hard ahead of the winter, when rebels retreat to hideouts.

Nato commanders have reported a huge increase in rocket attacks from Pakistani territory over the summer.

Pakistani officials have also complained about an increase in cross-border attacks from Afghanistan.