Mr Kerry said the two sides must decide “very quickly” how to proceed. North Korea has recently threatened nuclear attacks, and is feared to be preparing a missile launch.
A flurry of warlike statements from Pyongyang has prompted speculation that a launch could happen on 15 April, when the country marks the 101st birthday of the nation’s founder and former leader, Kim Il-sung.
North Korea has reportedly moved at least two Musudan ballistic missiles to its east coast, but on Saturday, South Korea’s Yonhap news agency quoted officials in Seoul as saying that no new movement of the mobile launchers had been detected for two days.
US officials including Mr Kerry have been playing down a leaked Pentagon report which warned that Pyongyang could have developed the technology to mount a nuclear warhead on a missile.
Since the UN imposed fresh sanctions on North Korea in February, its leadership has promised to restart a mothballed nuclear reactor, has shut an emergency military hotline to South Korea, and has urged diplomatic staff to leave, saying it cannot guarantee their safety.
The North says it has also been angered by joint US-South Korean military exercises.
Though its rhetoric has been more bellicose than usual, analysts say it fits a long-standing pattern, and may be intended to boost the popularity of Kim Jong-un, who came to power last year.
In Beijing Mr Kerry held talks with President Xi Jinping and Foreign Minister Wang Yi. In comments to Mr Xi, he said the world was facing “a critical time with some very challenging issues”.
Among them were Korean tensions but also “the challenge of Iran and nuclear weapons, Syria and the Middle East, and economies around the world that are in need of a boost”, he said.