A total of 13 military men, including three officers, were killed when an army helicopter they were traveling in crashed in Pakistan's northwest frontier province on Thursday, a military spokesman said.

The helicopter came down five kilometer southwest of Karak, a main city in the area, while on a routine flight.

"I can confirm that 13 army men, including three officers, were killed in the crash due to technical fault," spokesman Major General Shaukat Sultan said.

He said inquiry has been ordered to ascertain causes of the incident.

"It was a routine flight," the spokesman said.

Those died in the crash included one lieutenant general and two majors.

He said the pilot contacted his base and said that he was facing technical fault and had to go for emergency landing. "The helicopter crashed before landing," he said.

Sultan ruled out any terrorist act involved in the incident.

Meanwhile, a military official said three men tried to jump out of the helicopter before the crash. "Their bodied were un-burn," he said.

Another helicopter was following the first helicopter and the men on board did not see any firing, he said.

Eyewitnesses said they saw the helicopter caught fire after the crash at around 9:35 a.m. local time (0435 GMT).