China on Monday called for restraint after the United States flew a B-52 bomber over South Korea in a show of force to North Korea following its globally condemned fourth nuclear test.

"China wants to stay in communication with other parties and bring negotiations on the Korean Peninsula's nuclear issue back on track as soon as possible," Foreign Ministry spokesman Hong Lei told a regular news briefing. "We hope that relevant parties exercise restraint, take prudent actions and avoid ratcheting up tensions."

Hong also made very similar comments when asked about what China thinks of South Korea's resumption Friday of anti-North Korea propaganda broadcasts along its fortified border with the North in retaliation for the nuclear test.

Last Wednesday, North Korea said it had successfully conducted a hydrogen bomb test, in defiance of U.N. Security Council resolutions.

Though North Korea's most important political and economic backer, China has said it was not informed of Pyongyang's nuclear test plan in advance.

While China has been under growing international pressure to do more to restrict North Korea from taking provocative steps, the U.S. bomber flew over South Korea on Sunday, only four days after the test.

When North Korea conducted its third nuclear test in 2013, it took about a month for the United States to dispatch a bomber over South Korea to display its overwhelming military capability to Pyongyang.