The North Korean military is conducting intensive exercises as concerns are growing over the country's possible further aggression, a defense source told Yonhap news agency Wednesday.

"The North's winter military training, which began in early November, is extraordinarily active," said the source who asked not to be named.

The South Korean armed forces are keeping a close eye on the North's military moves, according to the source.

North Korea has significantly increased the number of drills of its special forces, in particular its airborne units.

This season, the number of parachute jump exercises using the radar elusive Antonov An-2 aircraft has risen more than 20 times than the previous year, according to the source.

As well, the North has doubled its live-fire artillery drills.

Another source said, "South Korea and the United States are closely monitoring the North Korean military's moves around the clock. But there is no indication of any imminent conflict with the North."

Meanwhile, North Korea has reportedly finished expansion of a major missile launch site near the border with China.

The country has also been enlarging a launch pad which apparently would be used for long-range rockets.

Pyongyang has also threatened to conduct another nuclear test in response to a UN resolution on its alleged human rights abuses.