Russia says it is in direct contact with North Korea to try to prevent it from carrying out its plan to test a nuclear weapon.
Mr Lavrov said North Korea must be persuaded back to talks
Russian Foreign Minister Sergei Lavrov said Moscow was talking to the North Korean leadership in an attempt to dissuade it from conducting a test.
Pyongyang's announcement on Tuesday triggered worldwide alarm.
South Korean Foreign Minister Ban Ki-moon said he was ready to travel to Pyongyang to try to resolve the crisis.
Mr Ban is the front-runner to replace Secretary General Kofi Annan, whose term expires at the end of the year.
In an interview published on Friday, Mr Ban told the Financial Times newspaper that in this role he would be "in a much better position to handle this issue" than Mr Annan.
Mr Lavrov, for his part, said Moscow was working directly with the North Korean government to ease the situation.
"We are all very worried about this," the minister told reporters while on a visit to Poland.
"We are talking about moves we can take and working directly with the leaders of North Korea to try to convince them to hold back from committing any act which could worsen the situation."
Mr Lavrov said that in the interests of the non-proliferation of nuclear weapons and security on the Korean peninsular, it was important that North Korea returned to the six-party negotiations.
North Korea says it possesses nuclear weapons, but this has not been independently verified.
Pyongyang has been involved in on-off six-party talks with Russia, the US, China, Japan and South Korea to resolve the crisis over its nuclear programme.
The most recent round of talks ended in September 2005, with a deal which promised economic aid in return for Pyongyang scrapping its nuclear ambitions.
That agreement, however, appears to have fallen apart over disagreements on its implementation.
North Korea has not specified where or when a nuclear test might be carried out.
US Secretary of State Condoleezza Rice said a nuclear test by North Korea would be a "very provocative act".
White House spokesman Tony Snow said on Thursday it was "enormously important" that North Korea was not allowed to develop nuclear weapons.
But he said US warnings did not amount to a "lethal threat" against Pyongyang.
In continuing diplomatic efforts to defuse the crisis, South Korean President Roh Moo-hyun is due to hold talks with US President George W Bush in Washington.
His visit comes amid talks of a split between Washington and Seoul on how to handle Pyongyang, after President Roh appeared to downplay North Korea's recent missile tests.