Washington, June 6 (IANS): Fresh activities have been detected around North Korea's main nuclear complex, housing its uranium enrichment facility, indicating some operations at the plant, a US monitor has said.

38 North, a website that monitors North Korea's activities, said on Wednesday recent commercial satellite imagery showed movement of vehicles, equipment and personnel near the uranium facility at Yongbyon, Yonhap news agency reported.

"Our observation that periodic material transport (possibly to deliver liquid nitrogen) has continued at the uranium enrichment complex over time provides a new indicator that the complex is operational and therefore it's also most likely producing enriched uranium," 38 North said on its website, citing satellite imagery from past months till May 28.

"However, we don't have any definitive means to determine either the actual levels of enrichment or the total production throughput of the around 4,000 centrifuges at this time," it said.

North Korea has built nuclear weapons from both plutonium and uranium and is estimated to have an arsenal of 20-30 nuclear weapons, the news agency said.

The report comes amid a stalemate in negotiations between Washington and Pyongyang, which was aimed at dismantling the North Korea's nuclear and ballistic missile programmes in exchange for sanctions relief.

At the second US-North Korea summit in February, the regime leader Kim Jong-un offered to dismantle the Yongbyon facility in return for easing of sanctions. But the meeting ended without any deal after the two sides failed to find common ground on the scope of denuclearisation and sanctions relief.

In March, the National Intelligence Service of South Korea was quoted by lawmakers as saying the North Korea's uranium enrichment facilities continued to operate normally and did so before the February summit as well.