The No. 2 U.S. diplomat urged China on Wednesday to "show leadership" on the North Korean nuclear issue, saying Beijing has more leverage over Pyongyang than any other country.

Deputy Secretary of State Tony Blinken issued the call shortly after talks with Foreign Minister Yun Byung-se and Vice Foreign Minister Lim Sung-nam in Seoul, where he is on a two-day visit to coordinate the allies' response to North Korea's fourth nuclear test on Jan. 6.

"China shares our commitment and our conviction that North Korea must denuclearize," he told reporters at the Foreign Ministry. "We believe that China has a special role to play, given the special relationship that it has with North Korea."

China is North Korea's last-remaining major ally.

"It has more influence and more leverage over North Korea than any other country because virtually all of North Korea's trade goes to, from or through China," Blinken said. "We are looking to China to show leadership on this issue."

Beijing has shown a lukewarm stance toward tough sanctions on Pyongyang out of concerns about its own national interests.

But China's role will be critical in drawing a strong sanctions resolution from the U.N. Security Council, as it is one of five permanent veto-wielding members.

Blinken said he will discuss the issue with Chinese officials when he visits Beijing later in the day.

U.S. Secretary of State John Kerry is also scheduled to visit China later this month.

Before coming to Seoul, Blinken visited Tokyo, where he held bilateral and trilateral talks with his South Korean and Japanese counterparts on the North's nuclear program and other issues. (Yonhap)