The United States continues to seek negotiations with North Korea to discuss a range of issues related to denuclearization, White House Press Secretary Jen Psaki affirmed Monday.

Her remark comes after the UN nuclear watchdog said the North appears to have restarted its plutonium-producing nuclear reactor at Yongbyon.

"We continue to seek dialogue with the DPRK so we can address this reported activity and the full range of issues related to denuclearization," Psaki said at a daily press briefing at the White House.

DPRK stands for the Democratic People's Republic of Korea, the North's official name.

The International Atomic Energy Agency (IAEA) said in an annual report to its board of governors that the Yongbyon reactor may have been in operation since July.

A senior US administration official on Sunday said the US was aware of the IAEA report and that it highlighted the urgent need for dialogue with North Korea.

Psaki reiterated the need to resume dialogue with Pyongyang.

"This report underscores the urgent need for dialogue and diplomacy, so we can achieve the complete denuclearization of the Korean Peninsula," she said.

North Korea has stayed away from denuclearization talks since leader Kim Jong-un's second summit with former US President Donald Trump ended without a deal in Hanoi in February 2019.

The first Kim-Trump summit was in Singapore in June 2018.

The top nuclear envoys of South Korea and the US met in Washington earlier in the day to discuss ways to bring North Korea back to the dialogue table.

Sung Kim, US special representative for North Korea, said the countries were discussing possible humanitarian assistance for the North to that end.

"We exchanged views on the situation on the ground, as well as some ideas and initiatives for engagement, including possible humanitarian assistance," he said of his second meeting with his South Korean counterpart, Noh Kyu-duk, in less than two weeks following his recent visit to Seoul.

"We also, of course, reaffirmed our shared commitment to pursuing the complete denuclearization of the Korean Peninsula through diplomacy, and I look forward to hearing back from the DPRK," Kim added.

The US envoy has repeatedly offered to meet with North Korean officials "anywhere, anytime" and without preconditions.

North Korea has largely remained unresponsive to overtures made by the Joe Biden administration since its inauguration in January. (Yonhap)