China's chief nuclear envoy, Wu Dawei, with his South Korean counterpart, Hwang Joon-kook, during a meeting at the Ministry of Foreign Affairs in Seoul, South Korea, on Februrary 28. REUTERS/Ahn Young-joon/Pool SEOUL/TOKYO — A Chinese envoy arrives in South Korea on Monday to discuss North Korea's increasingly defiant weapons program as a US Navy strike group heads to the region amid concerns Pyongyang may be readying a fresh nuclear test.

North Korea marks several major anniversaries this month and often marks the occasions with major tests of military hardware.

The possibility of US military action against North Korea in response to such a test emerged as an option following last week's US strikes against Syria. It was further fueled by comments from US President Donald Trump's top aides on the weekend.

In Tokyo, the feasibility of US military action was downplayed, while South Korea said the focus remained on deterrence and readiness.

"It probably is not realistic for the US to attack North Korea," a Japanese defense ministry source said. "If America says it is going to attack, both Japan and South Korea will probably put a stop to it," said the source, who declined to be identified.

US Secretary of State Rex Tillerson said the US military strike against Syria over its alleged use of chemical weapons was a warning to other countries including North Korea that "a response is likely" if they pose a danger.

Chinese President Xi Jinping "clearly understands, and I think agrees," Tillerson said on CBS' "Face the Nation," "that the situation has intensified and has reached a certain level of threat that action has to be taken."

China's special representative for Korean Peninsula affairs, Wu Dawei, is expected to discuss the North's nuclear issue with his South Korean counterpart, according to the South Korean foreign ministry.

Wu's trip comes after Trump and Xi met in Florida, where Trump pressed his counterpart to do more to curb North Korea's nuclear program.

President Donald Trump arriving at Joint Base Andrews in Maryland on Sunday. REUTERS/Carlos Barria

Show of force

The US Navy strike group Carl Vinson canceled a planned trip to Australia and is moving toward the western Pacific Ocean near the Korean peninsula as a show of force, a US official told Reuters over the weekend. "We feel the increased presence is necessary," the official said.

South Korean and US forces are also involved in annual joint military drills that run until the end of April. The North calls the drills preparations for war against it.

Several North Korean anniversaries in April could be opportunity for Pyongyang to conduct nuclear or missile tests, South Korean defense ministry spokesman Moon Sang-kyun said.

North Korea has invited a large number of foreign media representatives to Pyongyang this week, likely to cover the so-called Day of the Sun birth anniversary on Saturday of the state founder Kim Il Sung.

Moon did not directly respond to a question about the possibility of a US military strike against the North.

"Considering the possibility of North Korea's strategic provocations such as a nuclear test and missile launches, we have in place deterrence to the North's provocation and all readiness against them," he told a briefing on Monday.

Senior envoys of South Korea, Japan, and the United States on the North Korea nuclear program will soon meet to discuss their coordinated response, the South's foreign ministry said.

North Korea sounded a note of defiance Saturday, calling the US strikes against Syria "an unforgivable act of aggression" that showed its decision to develop nuclear weapons was "the right choice."

North Korea launched a ballistic missile on Wednesday that flew a short distance before spinning out of control and crashing into the sea, the latest of a number of missile tests defying UN sanctions.

The North is also seen to be ready to conduct its sixth nuclear test at any time, with movements detected by satellites at its Punggye-ri nuclear test site.

(Editing by Jack Kim and Lincoln Feast)