North Korea's chief nuclear envoy returned home Thursday from Beijing after holding unofficial talks with former U.S. diplomats in Singapore earlier this week over the North's nuclear and missile programs.

Upon his arrival at the Beijing airport before flying to Pyongyang, Ri Yong-ho, the North's chief negotiator to the long-stalled six-party talks on Pyongyang's nuclear weapons program, remained tight-lipped over whether he met with his Chinese counterpart, Wu Dawei, in Beijing.

A South Korean diplomatic source in Beijing downplayed the possibility of bilateral talks between Ri and Wu this week, saying, "To my knowledge, no talks between the chief nuclear envoys of North Korea and China were held this week."

Ri arrived in Beijing on Tuesday from Singapore, where he repeated North Korea's calls that Pyongyang would temporarily suspend nuclear tests if the United States halts joint military exercises with South Korea this year. Both Seoul and Washington rejected the proposal.

A former U.S. special envoy for North Korea policy, Stephen Bosworth, was among Ri's dialogue partners in Singapore on Sunday and Monday. The others included former deputy U.S. nuclear negotiator Joseph DeTrani and Leon Sigal, director of the Northeast Asia Cooperative Security Project at the Social Science Research Council.

Although the U.S. government was not involved, former American officials and North Korean diplomats have occasionally held unofficial talks to help the two governments better understand each other's positions.

The six-party denuclearization talks have been suspended since late 2008. (Yonhap)