The United States again downplayed last week's talks between North Korean diplomats and former US nuclear negotiators as "private" and "unofficial" discussions, urging Pyongyang to demonstrate denuclearization commitments so as to reopen the long-stalled nuclear negotiations.

"There's no US government involvement here. This is done by private citizens and typically they discuss a range of issues. But the United States government isn't sponsoring them. There's no government involvement in it," State Department spokesman John Kirby said at a regular briefing Monday.

Kirby was referring to the two days of meetings held in Malaysia's Kuala Lumpur last week between North Korean diplomats, including Vice Foreign Minister Han Song-ryol, and former nuclear negotiators Robert Gallucci and Joseph DeTrani.

The rare meetings drew keen attention as they could signal Pyongyang's willingness to reopen the long-stalled negotiations with the US amid heightened tensions in the wake of its fifth nuclear test and a series of missile launches.

The talks have also raised concern they could undermine international efforts to tighten sanctions on Pyongyang by giving an impression of flexibility on the part of the North. Both South Korea and the US have downplayed the talks as "Track 2" discussions unrelated to government.

"The Track 2 stuff is unofficial. It's private citizens and they talk about a range of issues. And as I said, they do this independent of any US government involvement," Kirby said.

He said the US is open to talks with the North, but said Pyongyang should prove it's serious about denuclearization.

"We remain open to dialogue with the DPRK with the aim of returning to credible and authentic negotiations about the denuclearization of the peninsula. But as we've also said, the onus is on the North to prove that they're able, willing and ready to join in those discussions through the six-party process, and they have not," he said. (Yonhap)