America's chief envoy to North Korea has warned that the future of six-nation talks on the North's nuclear programme is in doubt.
Christopher Hill says the US can't wait forever
Christopher Hill said Pyongyang was "ambivalent" about a negotiated settlement, but stressed the US was still committed to the talks process.
Tensions have risen recently, amid reports that Pyongyang might be preparing for a nuclear test.
But Seoul's security chief said on Wednesday there were no signs of this.
"So far, no unusual moves have been detected," Kwon Jin-ho was reported as saying by Yonhap news agency.
"Such talk stems from misgivings or apprehensions in a corner of the US. We don't need to take it seriously," he said.
US envoy Christopher Hill is touring North Asia for talks on how best to resolve the nuclear stand-off.
"The future of talks is very much uncertain at this point," Mr Hill told reporters as he left his hotel in Beijing on Wednesday.
Mr Hill said Washington, however, had not yet given up on the process. He has signalled that the US will not wait forever for Pyongyang to rejoin the talks, but would not be drawn on a deadline.
"I don't want to get into artificial deadlines. We continue to believe that this is the best way to solve this," he said.
Mr Hill also refused to speculate on Washington's options if Pyongyang does not return to diplomacy.
"We have a lot of options but one option we don't want is to walk away from this [the six party talks]."
If the US does decide to abandon the talks, it has suggested one course of action would be to seek further sanctions against North Korea at the UN Security Council.
Mr Hill's trip to China, which follows talks in South Korea, and precedes consultations in Japan, comes amid concerns that Pyongyang could be about to test a nuclear weapon.
American newspaper reports suggest there has been increased activity at North Korean sites where a nuclear test could be carried out.
Pyongyang has already said it possesses nuclear weapons, and that it intended to bolster what it calls its nuclear deterrent.
China has already hosted three rounds of six-way talks - which comprised delegates from the US, Japan, Russia, China and North and South Korea.
A fourth round of talks was due to be held last year, but did not take place because of Pyongyang's demand for concessions from the US and an end to what it called Washington's hostile policy.