LONDON: British Foreign Secretary Liz Truss warned on Wednesday it would be "a strategic mistake" by Moscow to invade Ukraine, amid concern at a Russian troop build-up on the border.

The message, delivered during a wide-ranging speech and question-and-answer session in London, follows similar warnings from Western capitals as tensions on the Ukrainian frontier.

Moscow has deployed up to 100,000 troops there in recent weeks, sparking fears of a major war in eastern Europe.

On Tuesday, President Joe Biden warned Russian President Vladimir Putin in a video link call of "strong" Western economic blowback against any attack on Ukraine.

The Kremlin leader demanded guarantees that the NATO alliance keep clear of Russia.

Russia planning Ukraine offensive with up to 175,000 troops: report

Truss, who is set to meet her Ukrainian counterpart Dmytro Kuleba later Wednesday, said Britain is "standing with Ukraine in the face of this aggression".

"I am very clear that it would be a strategic mistake for Russia to stage an incursion into Ukraine," she told an audience at the Chatham House international affairs think tank.

"The issue is not for Ukraine, the issue is for Russia to respect the sovereignty and territorial integrity of Ukraine," she said.

"The problem is that Russia has built up troops and forces on the Ukrainian border."

Truss, who replaced predecessor Dominic Raab as Britain's top diplomat in September, will host G7 and many southeast Asian foreign ministers at a UK summit this weekend when the issue will be further discussed.

In a speech billed as her first major foreign policy address, she said London wants to end the "strategic dependence" of a growing number of countries, such as Ukraine, on adversaries like Russia and China in various areas from energy to technology.

Truss noted the European Union relies on Moscow for over 40 percent of its gas, adding "with some countries Russia has a complete monopoly of supply".

"If Russia gets its way, Europe will be increasingly hooked on its gas. We have to end this strategic dependency -- whether it's on energy, investment or technology," she said.

"We have to provide an alternative and that means stepping up our engagement and our investments."

Truss added British foreign policy moving forward would be "unashamedly commercial" and pave the way towards "new tech, trade and security agreements".