US troops parachuted into North Korea: official

A senior US official has revealed that the US and South Korean special forces have been parachuting into North Korea to collect intelligence on underground military installations.

Brig Gen Neil Tolley, Commander of US special forces in South Korea, said in a conference in Florida recently that Pyongyang had built thousands of tunnels since the Korean war, reported a newspaper citing a magazine.

"The entire tunnel infrastructure is hidden from our satellites," Gen Tolley said. "So we send (South Korean) soldiers and US soldiers to the North to do special reconnaissance."

"After 50 years, we still don't know much about the capability and full extent" of the underground facilities," he said, in comments reported by a magazine on its website.

The commandos, according to Tolley, were sent in with minimal equipment to facilitate their movements and minimise the risk of detection by North Korean forces.

At least four of the tunnels built by Pyongyang go under the Demilitarised Zone separating North and South Korea, Tolley said.

"We don't know how many we don't know about," Tolley admitted.

Among the facilities identified are 20 air fields that are partially underground, and thousands of artillery positions.