GENEVA Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry expressed concern after North Korea conducted its fifth nuclear test on Friday.
Lavrov told reporters while meeting Kerry in Geneva to discuss Syria peace efforts that a message must be sent "very strongly" on implementing U.N. resolutions on North Korea.
Kerry said he expected President Barack Obama to address the issue on Friday and said there would be discussions at the United Nations.
"We're trying to monitor to precisely find out what took place," Kerry said.
"I'm very much concerned and the resolution of the Security Council must be implemented and we must send this message very strongly," Lavrov said when asked by a pool reporter about the test.
Kerry said he had talked on Friday to the foreign ministers of Japan and South Korea.
"We had a serious conversation about it. Obviously Japan and South Korea, particularly, are deeply concerned because of the neighbourhood. But I think it's fair to say China, Russia and the United States, everybody shares concerns about it," he said.
"At the appropriate moment today I'm confident President Obama will address (this) and we will certainly be discussing this in the context of the United Nations, for sure."
Earlier on Friday, Obama said any provocative actions by North Korea would have "serious consequences."
Obama had been briefed on board Air Force One by National Security Adviser Susan Rice about reported seismic activity near North Korea's nuclear test site earlier on Friday, White House press secretary Josh Earnest said.
North Korea set off a blast on Friday that was more powerful than the bomb dropped on Hiroshima, and said it had mastered the ability to mount a warhead on a ballistic missile.
Its most powerful explosion to date follows a test in January that prompted the U.N. Security Council to impose tightened sanctions that increased North Korea's isolation but failed to prevent it from accelerating weapons development.
North Korea's continued testing despite sanctions presents a severe challenge to Obama in the final months of his presidency and could become a factor in the U.S. presidential election in November.
(Reporting by David Brunnstrom; Editing by Dominic Evans)