Thirteen Pakistani troops, including three officers, were killed in a helicopter crash in the North West Frontier Province, defence ministry spokesperson Major General Shoukat Sultan said on Thursday.

A second helicopter following the ill-fated MI-17 landed and its personnel tried to carry out a rescue operation, but in vain.

Gen Sultan said the pilot of the helicopter reported technical problems to the ground control and headed for emergency landing before crashing into the mountains of Karak.

The helicopters were on a routine mission, he said.