South Korea and China have agreed that North Korea must immediately halt its nuclear activities and allow international inspectors to monitor the North's nuclear complex, Seoul's top nuclear envoy said Thursday.

Hwang Joon-kook, South Korea's top envoy for the long-stalled talks on North Korea's nuclear weapons program, said prospects about holding "exploratory talks" with the North are still uncertain because Pyongyang shows no signs of giving up its nuclear ambition.

"Both sides agreed that North Korea should swiftly carry out initial conditions for denuclearization, including a moratorium on its nuclear activities and returning the IAEA inspectors to its Yongbyon nuclear complex," Hwang told reporters after holding talks with his Chinese counterpart, Wu Dawei, in Beijing on Wednesday.

Hwang said China pledged to continue to "play a constructive role" in persuading North Korea to return to the negotiation table with sincerity on denuclearization.

The six-party talks aimed at persuading North Korea to give up its nuclear ambition, involving South Korea, North Korea, the United States, China, Japan and Russia, have been dormant since late 2008.

Since then, North Korea has advanced its nuclear capabilities by conducting its second and third nuclear tests, in 2009 and 2013.

Some experts now warn that the communist nation's nuclear arsenal could expand to 100 bombs by 2020.

In Washington on Tuesday, Hwang told reporters that five of the nations involved in the six-party talks are now ready to hold "exploratory talks" with North Korea without any preconditions to test the communist nation's denuclearization commitment before resuming formal negotiations.

Exploratory talks can take any format, multilateral or bilateral, Hwang said. (Yonhap)