The chief nuclear envoys of South Korea and China held talks on Friday as satellite images indicate that North Korea may be preparing to conduct its fifth nuclear test, possibly ahead of its key party congress early next month. 

Kim Hong-kyun, South Korea's Special Representative for Korean Peninsula Peace and Security Affairs, arrived in Beijing earlier in the day and began talks with his Chinese counterpart, Wu Dawei, said a South Korean diplomat who was involved in the Friday meeting.

Before departing for Beijing, Kim told Yonhap News Agency by telephone that he and Wu will have an "in-depth exchange of views on a range of cooperative measures, including an earnest implementation of U.N. Security Council resolutions, how to curb North Korea's additional provocations and countermeasures in the event of a North Korean provocation."

North Korea has been slapped with tough international sanctions following its fourth nuclear test in January and the launch of a long-range rocket in February.

Defying sanctions and international condemnation, North Korea has vowed to carry out more nuclear tests and ballistic missile launches.

Satellite images have shown that North Korea may have resumed tunnel excavation at its main nuclear test site.

North Korea is gearing up for a key party congress early next month with some analysts saying that Kim Jong-un may think that a fifth nuclear test is needed to burnish his credentials ahead of the May event.

On Thursday, Ambassador Sung Kim, the U.S. Special Representative for North Korea Policy, held talks with Wu in Beijing.

Kim said the U.S. and China "remain united on our firm opposition to North Korea's provocative and irresponsible behavior."

The U.S. and China "are deeply concerned" over signs of North Korea preparing for another nuclear test, Kim said, urging the North to refrain from making any such provocation. (Yonhap)