A nuclear-powered U.S. submarine made a port call in South Korea on Tuesday in a show of force amid concerns that North Korea may mark the foundation of its military with a missile launch or a nuclear test, defying U.S. and Chinese pressure.

The port call by the USS Michigan came as a U.S. aircraft carrier strike group steams for Korean waters and as the top nuclear envoys from South Korea, Japan, and the United States were to meet in Tokyo to discuss the North's refusal to give up its nuclear programme.

Japan's Chief Cabinet Secretary, Yoshide Suga, told a media briefing that China's nuclear envoy, Wu Dawei, would also hold talks with Japanese Foreign Ministry officials on Tuesday. A ministry source said Mr. Wu was likely to meet his Japanese nuclear counterpart on Wednesday.

Matching the flurry of diplomatic and military activity in North Asia, the State Department in Washington said on Monday U.S. Secretary of State Rex Tillerson would chair a special ministerial meeting of the U.N. Security Council on North Korea on Friday.

Mr. Tillerson, along with Defense Secretary Jim Mattis, Director of National Intelligence Dan Coats and Joint Chiefs chairman General Joseph Dunford, would also hold a rare briefing for the entire U.S. Senate on North Korea on Wednesday, Senate aides said.

On Monday, U.S. President Donald Trump called for tougher new U.N. sanctions on Pyongyang, saying the North was a global threat and “a problem that we have to finally solve”.

“The status quo in North Korea is also unacceptable,” Mr. Trump told a meeting with the 15 U.N. Security Council ambassadors, including China and Russia, at the White House. “The council must be prepared to impose additional and stronger sanctions on North Korean nuclear and ballistic missile programs.”

South Korean and U.S. officials have feared for some time that a sixth North Korean nuclear test could be imminent. Speculation has grown that such a test, or another long-range missile launch, could coincide with the 85th anniversary of the foundation of the North's Korean People's Army on Tuesday.

“Seriously misread”

The official China Daily said on Tuesday it was time for Pyongyang and Washington to take a step back from harsh rhetoric and heed the voices of reason calling for a peaceful resolution.

“Judging from their recent words and deeds, policymakers in Pyongyang have seriously misread the U.N. sanctions, which are aimed at its nuclear/missile provocations, not its system or leadership,” the newspaper said in an editorial.

“They are at once perilously overestimating their own strength and underestimating the hazards they are brewing for themselves,” it said.

In a phone conversation with Trump on Monday, Chinese President Xi Jinping called for all sides to exercise restraint.

Two Japanese destroyers conducted exercises on Monday with the USS Carl Vinson aircraft carrier strike group that is headed for waters off the Korean peninsula, sent by Trump as a warning to the North.

The South Korean military is also planning to conduct joint drills with the carrier group.

As those drills continued, the USS Michigan arrived in the South Korean port of Busan on Tuesday, the U.S. Navy said. The nuclear-powered submarine is built to carry and launch ballistic missiles and Tomahawk cruise missiles.

As well as his military show of force, Mr. Trump has also sought to pressure China to do more to rein in its nuclear-armed neighbour.

China, North Korea's sole major ally, has in turn been angered by Pyongyang's belligerence, as well as its nuclear and missile programmes.

Regardless, North Korea has carried out nuclear and missile tests in defiance of successive rounds of United Nations sanctions.

Angered by the approach of the carrier group, which could arrive within days, North Korea said the deployment of the USS Carl Vinson was “an extremely dangerous act by those who plan a nuclear war to invade".

“The United States should not run amok and should consider carefully any catastrophic consequence from its foolish military provocative act,” Rodong Sinmun, the official newspaper of North Korea's ruling Workers' Party, said in a commentary.