Seoul: North Korea issued warning on Saturday that its military would not remain a "passive onlooker" if South Korea and the United States continued their joint military drills.

The threat has been made by Ri Yong-Ho, a vice marshal of the North's armed forces, at a meeting attended by top government, military and party officials in Pyongyang.

In his speech, Ri said that North Korean troops and people would not remain "passive" onlookers to what he called "provocative and aggressive nuclear war exercises" being staged by US and South Korean troops.

"National defence is the most important affair in building a thriving nation," Ri said.

This year South Korea has been staging a series of drills alone or together with US troops to test its battle readiness.

The troops of US and South Korea completed computerized joint war games on March 10, but joint field training will continue throughout April.

South Korean Defence Minister Kim Kwan-Jin said that this week the North may attempt surprise attacks across the sea border after practising marine infiltration drills.

He warned of the possibility of "various types of surprise local provocations".