American and South Korean forces have carried out joint air infiltration drills simulating entry into North Korea in the case of a full-fledged war in the Korean peninsula. About 250 South Korean soldiers boarded several helicopters in the mock drill, which simulated penetrating North Korean territories.

More than a dozen helicopters – including the UH-60 Blackhawk, CH-47 Chinook and AH-1S Cobra – were used by military forces in the exercises. The joint forces and special units were tasked with knocking out Pyongyang's key communication facilities in a war situation.

A South Korean army spokesperson told the Yonhap news agency that the helicopters took off from the town of Chungju, 147km south of the capital Seoul, and wrapped up their drills in Hongcheon, 102kms east of the city.

The South Korean military and US forces have been placed on high alert in the peninsula as Pyongyang is expected to conduct a missile or even a nuclear test to coincide with the US presidential election. The reclusive kingdom has conducted two major nuclear tests and more than a dozen missile launches in 2016 alone, chiefly as a show of strength to its arch enemy in the divided peninsula.

"We are closely watching every move by the North Korean military at its Punggye-ri nuclear test site and other possible missile-launching sites. The military is fully prepared to respond to any provocative acts by the North," an official with Seoul's Joint Chiefs of Staff (JCS) told reporters.