Dozens of top South Korean military officials have spent their weekend leisurely playing golf amid high tensions in the Korean peninsula over Pyongyang's threats at the joint military drill.

The Presidential office in Seoul has launched an immediate inquiry into the local reports as the US-South Korea joint military exercise is underway.

"Cheong Wa Dae is paying particular attention to the issue of discipline slackening in public service. The office of the senior civil affairs secretary has immediately launched an inquiry to determine what has exactly happened regarding the reports about military golf," said the presidential spokesperson Yoon Chang-jung.

Some of the high-ranking generals are also involved, it has been said.

The reports have come at a time when Washington and Seoul has begun its joint military drills in the Korean peninsula.

Hours ahead of the drills, North has also severed the emergency hotline with Seoul, as it had earlier threatened.

Seoul's unification ministry has announced that Pyongyang appears to have disconnected the inter-Korean communication hotline following the attempts to contact the defiant nation failed.

The cross-border link was set-up in 1971 to deal with any developments at the demilitarised zone separating the two countries.

North has also announced that the non-aggression pacts between two Koreas are null and void starting from 11 March.

Key Resolve, the computer-simulated annual exercise jointly conducted by Seoul and Washington will go on till 21 March. Pyongyang is also gearing to conduct a nationwide military drill, further increasing the tensions.

Seoul military sources have hinted a "possible attack" by the North Korean forces during the drill, suggest local reports.

On the eve of the drill, North's mouthpiece Rodong Sinmun said, "Our front-line military groups, the army, the navy and the air force, the anti-aircraft units and the strategic rocket units, who have entered the final all-out war stage, are awaiting the final order to strike."

South Korean military has also increased its surveillance on the North's movements and are in full preparedness over the ongoing situation. South's new president Park Geun-hye earlier said the current situation is "very grave."

Pyongyang was angered by the recent UN sanctions which tightened the screws on its finances to punish for its third nuclear test conducted on 12 February.