Chinese President Xi Jinping and Japanese Prime Minister Shinzo Abe both spoke with Trump by phone on Monday amid concerns Pyongyang might carry out another nuclear test this week, in defiance of UN sanctions.

According to a statement from the Chinese foreign ministry, Xi told Trump that China opposes any actions that run counter to UN Security Council resolutions.

"[China] hopes that all relevant sides exercise restraint, and avoid doing anything to worsen the tense situation on the peninsula," Xi was paraphrased as saying.

Watch video 00:20 North Korea arrests another US citizen

Despite condemning the belligerence of North Korea, China remains its only major ally and economic lifeline, and fears what may happen if its poverty-plagued neighbor wages war or collapses.

In a statement, the White House said that Trump, in his phone call with Xi, had criticized North Korea's "continued belligerence."

"The two leaders reaffirmed the urgency of the threat posed by North Korea's missile and nuclear programs, and committed to strengthen coordination in achieving the denuclearization of the Korean peninsula," the statement read.

Talks with Japan

Earlier, Trump and Japanese Prime Minister Shinzo Abe agreed over the phone to maintain close contact on the issue.

"We agreed to strongly demand that North Korea, which is repeating its provocation, show restraint," Abe told reporters Monday, adding that he and Trump also agreed China should play a larger role in dealing with Pyongyang.

North Korea's reclusive regime, led by Kim Jong Un, often conducts its weapons tests to coincide with days of national significance. On Tuesday the country marks the 85th anniversary of its army's founding.

Military drills

Two Japanese destroyers on Sunday began training exercises in the western Pacific with a group of warships from the US including the aircraft carrier USS Carl Vinson, which US Vice President Mike Pence on Saturday said would be in the Sea of Japan within "days."

North Korea condemned the deployment as "an extremely dangerous act" in a commentary published in "Rodong Sinmun," the official newspaper of its ruling party.

"The United States should not run amok and should consider carefully any catastrophic consequence from its foolish military provocative act," the newspaper said.

The tensions on the Korean peninsula were heightened further when Pyongyang reportedly detained a US citizen as he was leaving the country.