China on Tuesday called for more efforts to ease tension over the Korean Peninsula nuclear issue and settle it through dialogue, after US President Donald Trump designated the Democratic People's Republic of Korea as a state sponsor of terror, moving the country back into a list which also includes Iran, Sudan and Syria.

"Currently, the situation on the Korean Peninsula is complicated and sensitive," Foreign Ministry spokesman Lu Kang told a news conference in Beijing on Tuesday.

"We hope all relevant parties can do more to ease the tension and do more that is conducive to returning to the correct path of negotiation and consultation to resolve the peninsula's nuclear issue," he said.

Trump said in Washington on Monday that "we will be instituting a very critical step, and that will start right now. Today, the United States is designating North Korea as a state sponsor of terrorism".

"It should have happened a long time ago. It should have happened years ago," said Trump, accusing the DPRK of "threatening the world by nuclear devastation" and repeatedly supporting "acts of international terrorism, including assassinations on foreign soil".

White House officials previously blamed Pyongyang for killing a man in a Malaysia airport and murdering the US citizen Otto Warmbier, both denied by Pyongyang.

Warmbier was a US university student who, while visiting the DPRK as a tourist in January last year, was arrested and sentenced to 15 years imprisonment.

He was released in June and died six days after he returned to the US.

"As we take this action today, our thoughts turn to Otto Warmbier, a wonderful young man," Trump said, vowing to impose further sanctions and penalties on Pyongyang and related people.

Trump also said the US Treasury Department will announce measures on Tuesday to slap an additional "large" sanction against the DPRK.

The DPRK "must be lawful", he said, adding that "it must end its unlawful nuclear and ballistic missile development, and cease all support for international terrorism - which it is not doing".

Largely symbolic

However, US experts and officials argued on condition of anonymity that Pyongyang does not meet the criteria for the designation, which requires evidence that a country has repeatedly provided support for acts of international terrorism.

The move will be largely symbolic, as Pyongyang has already been heavily sanctioned, the experts said.

Washington has sent three aircraft carrier battle groups earlier this month to the waters near the peninsula, the first of such scale in 10 years, to conduct a military exercise.

For its part, Pyongyang on Friday said that instead of urging the DPRK to return to talks, Washington should repent its action that put the peninsula in danger of a nuclear war.

The DPRK was removed from the list by then-US president George W. Bush in 2008 to assist resolution of the nuclear crisis.

Xinhua contributed to this story.