The United States on Tuesday called on China and Russia to do more to rein in North Korea, after Pyongyang announced it would restart a nuclear reactor to feed its atomic weapons program.
White House spokesman Jay Carney said the North's decision to reopen its Yongbyon reactor -- its source of weapons-grade plutonium -- was "another indication" of Pyongyang "violating its international obligations."
"It is not a mystery to anyone that China has influence with North Korea," Carney told reporters.
"We have in the past and are now urging China to use that influence to try to affect North Korean behavior. That is also true of our (conversations) with the Russians."
Beijing has already voiced regret over North Korea's announcement, appealing for calm on the Korean peninsula.
The crisis was due to dominate talks later Tuesday in Washington between US Secretary of State John Kerry and his South Korean counterpart Yun Byung-se.
The Korean peninsula has been caught in a cycle of escalating tensions since a February nuclear test, which followed a long-range rocket launch in December, by North Korea, also known as the DPRK.
The meeting comes ahead of Kerry's visit to the region next week -- his first to Asia since taking over as the top US diplomat in February -- when he will travel to South Korea, China and Japan.
State Department spokeswoman Victoria Nuland on Tuesday reiterated Washington's position that "the United States will not accept the DPRK as a nuclear state."
But she stressed that despite Pyongyang's newest threat "there's a long way to go between a stated intention and actually being able to pull it off.
"Were they to be able to put themselves back into a position to use the facility, that would obviously be extremely alarming. But as I said, it's a long way from here to there," she said.