South Korea and the U.S. agreed Friday to cooperate more closely on the adoption of a strong U.N. sanctions resolution against North Korea following its fourth nuclear test, the Foreign Ministry said.

Foreign Minister Yun Byung-se and U.S. Secretary of State John Kerry held phone talks earlier in the day to discuss Kerry's trip to Beijing earlier in the week.

During the 20-minute discussion, the two sides shared opinions on Kerry's visit to China and coordinated their responses to North Korea's Jan. 6 nuclear test and the possibility of further provocations from the North, the ministry said in a press release.

Kerry said he told Chinese government officials that Washington places top priority on the North Korean nuclear issue as the recent test poses a major threat to international peace and security, and especially those of the U.S. mainland and its allies, according to the ministry.

He also expressed the U.S.'s firm resolve to do everything it can to protect its allies.

"The two ministers agreed to take more specific steps in cooperation between the U.S. and China as well as coordination between South Korea and the U.S. for the adoption of a U.N.

Security Council resolution," the ministry said.

Kerry added that the U.S. and China agreed to accelerate bilateral talks at the U.N. and through other channels to adopt a strong resolution.

Kerry's trip, during which he held talks with Chinese Foreign Minister Wang Yi and other senior officials, underscored the large differences between the two countries over the appropriate level of sanctions on North Korea.

China has been reluctant to push the North too hard out of concerns for its own security interests, including the possibility of an influx of North Korean refugees or a U.S.-allied, unified Korea at its borders.

Its cooperation is critical, however, in drawing tough sanctions from the U.N. Security Council because it is one of five permanent veto-wielding members, along with the U.S., Russia, France and Britain.

On the possibility of a long-range missile launch by the North and other provocations, Yun and Kerry agreed to seek necessary relevant measures, the ministry said.

Yun and Kerry have held three phone conversations since the North's nuclear test. They agreed to continue their close coordination through further talks at the Munich Security Conference next month. (Yonhap)