Adding to the tension, North Korea detained a USA citizen on Saturday as he attempted to leave the country.
"We call on North Korea to refrain from provocative, destabilising actions and rhetoric, and to make the strategic choice to fulfill its global obligations and commitments and return to serious talks", CNN quoted Pentagon spokesman Gary Ross as saying.
Two Japanese destroyers have joined the US carrier group for exercises in the western Pacific, and South Korea said it was in talks about holding joint naval exercises.
North Korea claims the US has created a situation in which "nuclear war could break out at any time", NBC reported.
China "hopes that all relevant sides exercise restraint, and avoid doing anything to worsen the tense situation", the Chinese ministry said in a statement, paraphrasing Xi.
On Monday, the Global Times newspaper said that if North Korea stages a sixth nuclear test, Beijing would "undoubtedly support" the United Nations in adopting tougher sanctions against the regime, including an embargo on oil exports.
The nuclear issue could be resolved quickly only with all relevant countries pulling in the same direction, and China was willing to work with all parties, including the United States, to ensure peace, Xi said.
The United States and its allies fear North Korea could be preparing to conduct another nuclear test or launch more ballistic missiles. This indicated that North Korea was developing technologies to "cold-launch" ICBMs, ejecting them from the launch tubes before they ignite in midair, which would prevent its limited number of ICBM-capable launcher trucks from being damaged and also allow the missiles to be fired from silos.
The U.N. has demonstrated its "utmost concern over the Democratic People's Republic of Korea's highly destabilizing behavior and flagrant and provocative defiance of the Security Council", CNN reported. North Korea marked its most recent holiday, the 105th anniversary of the birth of North Korean founder Kim Il Sung, on April 15 with a massive military parade, a video featuring a simulated nuclear strike on an American city, and a missile test.
While Trump has dispatched what he called an "armada" of ships to the region, including an aircraft carrier, USA officials have told The Associated Press that the administration doesn't intend to militarily respond to a North Korean nuclear or missile test.
China's Defense Ministry denied media reports last week it had put its troops on "high alert" near the North Korea border, saying it was merely conducting "normal training".
Fresh off an huge North Korean parade that revealed an arsenal of intercontinental ballistic missiles, rival South Korea and its allies are bracing for the possibility that Pyongyang's follow-up act will be even bigger.
Asked whether a pre-emptive strike was under consideration, she said: "We are not going to do anything unless he gives us reason to do something".
"If you see him attack a military base, if you see some sort of intercontinental ballistic missile, then obviously we're going to do that".
Earlier, Japanese Prime Minister Shinzo Abe described his conversation with Trump as a "thorough exchange of views".
"We completely agreed that we strongly demand restraint by North Korea, which has repeatedly taken risky provocative actions", Abe told reporters after the call.
Trump has pressed Xi to exert greater pressure against North Korea, given China's status as the country's sole economic lifeline and major ally.
North Korea separately fired what US officials said were a Scud-type missile and a midrange missile earlier this month, but the launches were analyzed as failures.