A US B-1B bomber on Wednesday joined large-scale US-South Korean military exercises that Pyongyang has denounced as pushing the peninsula to the brink of nuclear war.
The bomber flew from the Pacific US-administered territory of Guam and joined US F-22 and F-35 stealth fighters in the annual exercises, which run until Friday.
The drills come a week after North Korea said it had tested its most advanced intercontinental ballistic missile capable of reaching the United States as part of a weapons program that it has conducted in defiance of international sanctions and condemnation.
Asked about the bomber's flight, Chinese Foreign Ministry spokesman Geng Shuang told a regular news briefing in Beijing: "We hope relevant parties can maintain restraint and not do anything to add tensions on the Korean peninsula."
North Korea regularly threatens to destroy South Korea, the United States and Japan and its official KCNA state news agency said at the weekend US President Donald Trump's administration was "begging for nuclear war" by staging the drills.
It also labeled Trump, who has warned to destroy North Korea if the US is threatened, "insane".
Also Wednesday, North Korea's vice foreign minister met visiting UN political affairs chief Jeffrey Feltman in Pyongyang, the North's state media said.
The North Korean official, Pak Myong Guk, and Feltman discussed bilateral cooperation and other issues of mutual interest, the KCNA news agency reported.
Feltman, a former senior US State Department official, is the highest-level UN official to visit North Korea since 2012.
Meanwhile, the North Korean ballistic missile was seen by the crew of several airliners last week, aviation authorities said Wednesday, raising concerns about the threat to civilian flights posed by Pyongyang's unannounced tests.
"A Korean Air jet flying to Incheon from San Francisco reported to Japanese controllers that its flight crew saw a flash from what was believed to be the North Korean missile," a Korean Air spokesman told AFP.
Four minutes later another Korean Air plane on a Los Angeles-Incheon flight also reported the same sighting to Japanese control, he said.
A South Korean transportation ministry official, who wanted to remain unnamed, said the flight paths of both Korean airlines were some 220 kilometers away from where the missile landed.
"In the clean dark sky, you can see flashes from a missile from that long distance," he told AFP.
The UN's International Civil Aviation Organization (ICAO) in October condemned the North's continued unannounced missile launches, urging it to comply with international aviation standards to prevent risks.
South Korean authorities said they warned airlines of a possible missile test a day before the launch based on intelligence reports, the transportation ministry official said.