A senior diplomat from North Korea involved in stalled international talks to end its nuclear programme has visited China, a South Korea news agency said on Wednesday, as China endorsed a fresh rebuke of the North by the United Nations.

The UN Security Council issued its latest condemnation of the North after it conducted ballistic missile test launches on Monday. China, the reclusive North Korea's main diplomatically, joined the criticism.

North Korean diplomat Choe Son Hui arrived in Beijing on Tuesday with her interpreter, the South's Yonhap news agency cited an anonymous source familiar with the situation in North Korea as saying.

Yonhap did not specify the reason for her trip or say who she was expected to meet.

Choe is deputy director-general of the North Korean foreign ministry's US affairs bureau, according to South Korea.

She was the deputy chief envoy to negotiations known as six-party talks, hosted by China and including the two Koreas, Japan, Russia and the United States, aimed at getting the North to give up it nuclear aims but stalled since 2008.

Asked about the visit at a daily news briefing in Beijing, Chinese Foreign Ministry spokeswoman Hua Chunying said she had no information.

Choe visited Beijing in June to take part in a forum attended by nuclear envoys of the United States and South Korea but was not reported to have engaged in government-level discussions.

Chinese President Xi Jinping reaffirmed the country's commitment to denuclearising the Korean peninsula at talks with South Korean President Park Geun-hye on Monday on the sidelines of a G20 summit in the Chinese city of Hangzhou.

North Korea has become even more isolated after a January nuclear test, its fourth, and the launch of a long-range rocket in February brought tighter UN Security Council sanctions that the North subsequently defied with more missile launches.

China disapproves of the North's missile and nuclear programmes and backed the Security Council resolutions in March.

North Korea tested three ballistic missiles on Monday, firing them into the sea off its east coast as China was hosting the G20 summit.