The crisis began when South Korea's 1,200-ton Cheonan corvette sank near the disputed Northern Limit Line in the Yellow Sea on March 26, causing the loss of 46 lives.

Although initial comments from South Korean naval and intelligence chiefs ruled out foul play, after an international investigation Seoul accused North Korea of firing a torpedo from a submarine at the vessel.

Pyongyang claims the incident was "orchestrated" by the United States in order to "hype the threat from North Korea" ahead of "Congress mid-term elections slated for the coming November."

"The situation is really explosive; everything necessary should be done now... to complete the investigation... and think of how to continue the six-sided talks and achieve the denuclearization of the Korean Peninsula," Sergei Lavrov told a news conference.

"Russia believes it is of principled importance not to let this important task out of sight," he said.

Following the investigation, South Korea froze economic relations and maritime communications with its northern neighbor, further crippling the North's economy, which is already damaged by UN sanctions intended to force it to quit its nuclear program.

North Korea retaliated by announcing it was cutting all ties with Seoul and reportedly ordered its 1.2-million-strong armed forces to get ready for war. It later announced the withdrawal of all its military safeguards in relations with the South and said it would scrap an agreement between the two countries aimed at preventing clashes off the west coast.