Russia said it hoped forthcoming talks in Moscow with US Secretary of State Rex Tillerson would be productive, but said it was extremely worried the United States might decide to unilaterally attack North Korea.

North Korea is emerging as one of the most pressing foreign policy problems for US President Donald Trump. Pyongyang has conducted five nuclear tests and is working to develop nuclear-tipped missiles that can reach the United States.

A US official told Reuters over the weekend that a US Navy strike group led by a nuclear-powered aircraft was steaming towards the western Pacific as a show of force.

Tillerson, on his first visit to Moscow as secretary of state, is due to hold talks with Sergei Lavrov, his Russian counterpart, on Wednesday at a time when US-Russia ties are languishing at a post Cold War low.

The Russian foreign ministry, in a statement ahead of his visit, said it was concerned about many aspects of US foreign policy, including on Libya, Yemen and Syria, but said it was particularly concerned about North Korea.

“We are really worried about what Washington has in mind for North Korea after it hinted at the possibility of a unilateral military scenario,” the statement said.

“It's important to understand how that would tally with collective obligations on denuclearising the Korean peninsula, something that is underpinned in UN Security Council resolutions.”

Russia slammed US cruise missile strikes on a Syrian air base on Friday calling them an illegal attack on a sovereign state.

There are growing fears in Moscow that Trump, who it once thought would be isolationist, is becoming increasingly confident about using force to achieve his foreign policy goals.

Russian foreign ministry said on Tuesday it hoped the United States would agree to an international investigation of the nerve gas attack which prompted the US missile strike on Syria and that US officials would also take part in Afghanistan talks in Moscow later this week.