The official made the remark during a conference call with reporters to preview Kerry's trip to Beijing set to begin Wednesday, stressing the need for presenting a united front to the North in the wake of the communist nation's fourth nuclear test.

"The pre-eminent issue ... is the question of how China, in tandem with international partners and on a bilateral basis -- or I should say perhaps a unilateral basis -- can convince the DPRK to reverse course, to come into compliance with its international obligations and its own commitments, and to be in the process of rolling back its nuclear and its missile program," the official said on condition of anonymity.

Kerry has made no secret of his conviction that there is "much more that China can do by way of applying leverage," the official said, adding that the top American diplomat will be looking for practical and effective steps on the part of the Chinese.

The U.N. Security Council has been discussing sanctions on the North, and those negotiations will likely "play out for a little longer," the official said. Kerry and his Chinese counterparts will "compare notes on where that stands and what we can do by the Security Council," the official said.

But as important as U.N. sanctions are "what China on a unilateral basis, as North Korea's lifeline, as North Korea's patron, will choose to do, both to cut off avenues of proliferation and retard North Korea's ability to gain the wherewithal to advance its nuclear and its missile programs" is even more important, the official said.

It is also important to "send an unmistakable message to Kim Jong-un that his strategy is meeting with real resistance from China," the official said.

China has made efforts to prevent illegal activities and proliferation from the North via "Chinese soil, Chinese ports, Chinese banks and Chinese companies," but there is still much more room for more efforts, the official said.

"North Korea is still engaged in illicit and proliferation activities. They have very few avenues for conducting business with the international community that don't in some fashion involve transiting China," the official said.

"Despite the determination and efforts of the Chinese government, clearly there is more that they can do. And I certainly hope that in the aftermath of this latest nuclear test that the Chinese are examining those conduits and avenues and looking for ways to intercept and restrict North Korean proliferation activities," the official said.

The official also emphasized that the U.S. has tried to hold negotiations with the North, but it is the communist nation that walked away and keeps "saying no to proposals from all quarters that we negotiate, as they committed to, to eliminate their nuclear missile program."

"We want them to walk back, and it's both pressure and incontrovertible evidence that the international community isn't going to change its mind and decide that we're good with a nuclear North Korea. That's not going to happen, and the Chinese don't want it either," the official said.

On the issue of American citizens detained in North Korea, the official said the U.S. is working hard to secure their release through the Swedish Embassy in Pyongyang, which serves as the protecting power for the U.S. The U.S. also conveys its concerns directly to the North, the official said. (Yonhap)