China's special representative for the Korean Peninsula, Wu Dawei, met with his Japanese counterpart Tuesday to show a concerted effort to deal with North Korea's growing nuclear ambitions.

The meeting comes at a time when the efficacy of recent United Nations sanctions hinges largely on China's thorough implementation of them.

In talks with Kimihiro Ishikane, director-general of the Foreign Ministry's Asian and Oceanian Affairs Bureau, Wu agreed that they will closely cooperate in implementing the U.N. resolution, which imposed the toughest sanctions on the North to date.

"China and Japan agreed that we will have close consultation on this issue," Wu told reporters after the meeting, which lasted more than 90 minutes.

This is the first time Wu has visited Japan in his official capacity since Prime Minister Shinzo Abe took office in December 2012. He also visited South Korea in late February for the first time in almost five years.

Wu's active diplomacy implies that Beijing wants to exert its influence over the North, though Beijing has to perform a delicate balancing act as both Pyongyang's biggest economic partner and a permanent seat holder at the U.N. Security Council.

A month after the U.N. resolution was adopted unanimously, Pyongyang's provocative acts continue, and its attitude toward China has hardened.

In a rare and only slightly veiled criticism of China on Monday, Rodong Sinmun, the official newspaper of North Korea's Workers' Party, said a big country that values saving face gave in to the threats and demands of the U.S., abandoning its friendship with the North.

Also on Monday, 38 North, a U.S. website monitoring North Korea, said recent satellite imagery showed "suspicious activity" at the country's nuclear complex, a sign Pyongyang might be enriching weapons-grade plutonium from spent nuclear fuel.

During the Nuclear Security Summit, which ended Friday in Washington, U.S. President Barack Obama and Chinese President Xi Jinping agreed to full implementation of the U.N. sanctions while Japan, the U.S., and South Korea pledged in their trilateral meeting to walk in lockstep to counter Pyongyang's nuclear provocations.

Yet China, which shares a border with the impoverished nation, has maintained the importance of conducting talks with Pyongyang.

Ahead of Wu's visit, Chinese foreign ministry spokesman Hong Lei said on Friday that Wu planned to discuss the resumption of six-party talks, which are aimed at denuclearizing the Korean Peninsula.

The talks, which involve North Korea, South Korea, China, the U.S., Russia and Japan, have been stalled since late 2008.

Wu did not say he and Ishikane discussed the six-party talks, but countries such as the U.S. and Japan have been reluctant to hold talks with the defiant North unless it demonstrated a step toward denuclearization.

"I do think the six-party talks are an effective framework," Foreign Minister Fumio Kishida told reporters Tuesday. "Yet given the current situation, North Korea should first take positive and constructive measures toward denuclearization of the Korean Peninsula."

Meanwhile, Wu's visit also came five days before the Group of Seven foreign ministers' meeting kicks off in Hiroshima, where Japan hopes to bring up various issues, including simmering tensions in the South China Sea. Asked about the nautical disputes, Wu said, "Japan has nothing to do with the South China Sea."

Although Japan is not directly involved with the South China Sea, where Beijing is engaged in land-reclamation projects, China has been alarmed by the actions of Japan's Self-Defense Forces, which have been loaning defense equipment and providing capacity-building to Southeast Asian countries.

On Sunday, the Maritime Self-Defense Force training submarine Oyashio made a goodwill visit to the Philippines for the first time in 15 years together with the destroyers Ariake and Setogiri.

Despite the underlying tensions, Kishida emphasized that bilateral relations with China were generally improving, and he still hoped to visit Beijing during the spring.

Wu said that Chinese Foreign Minister Wang Yi welcomed Kishida's possible visit and the two countries were working to coordinate it.