U.S. Secretary of State John Kerry and his Chinese counterpart, Yang Jiechi, agreed Tuesday that the world's two supreme powers need to work together to deal with North Korea's threats to carry out another nuclear test.

The two discussed North Korea and other pending issues over the phone "for quite a while," Kerry's department said.

"They agreed on the importance of continuing to work to strengthen U.S.-China relations, notably including in the economic, trade and investment sphere. They also discussed the continued provocative rhetoric coming from the DPRK," State Department spokeswoman Victoria Nuland said at a press briefing, referring to North Korea.

It was the first conversation between Kerry and Yang since the former U.S. senator succeeded Hillary Clinton on Friday.

The two sides agreed to ensure that North Korea face "further consequences" if it again violates its international obligations.

The U.N. Security Council adopted a set of new sanctions on Pyongyang last month for its Dec. 12 long-range rocket launch.

The communist nation reacted with a series of threats to fire more rockets and conduct what would be its third nuclear experiment, following two detonations in 2006 and 2009.

Kerry and Yang agreed that all relevant parties must "stay united" in handling North Korea.

As reporters recalled Kerry's phone talks with his South Korean and Japanese counterparts last week, Nuland emphasized "the conversation was remarkably similar."

China is arguably the most important party in efforts both to dissuade North Korea from conducting a nuclear test and then to take punitive measures afterwards.

The international community is especially concerned that the secretive North may be planning a uranium explosion.

If that is the case, it will serve as a "game-changer" and pose greater challenges, experts say.

If Pyongyang detonates a nuclear bomb again, based either on plutonium or uranium, the U.N. Security Council is certain to push for tougher sanctions, including the expansion of financial sanctions and inspections of almost all North Korean trade.

"These sanctions would require China to play an enforcement role against North Korean economic actors it has hitherto resisted," North Korea expert George Lopez said in an op-ed piece on CNN's website.

China has been traditionally uncooperative in pushing North Korea too hard, however, apparently due to worries over political and further economic instability in the communist neighbor.

Lopez said Beijing "might well accept specialized trade sanctions" based on precise lists of dozens of the materials used in centrifuge operation.

"Also critical to the success of this choking of supplies would be stricter controls of the illicit financing that supports such trade," he added. (Yonhap News)