The West must ensure that Russian President Vladimir Putin be defeated in Ukraine and needs to continue supporting Kyiv without any backsliding, British Foreign Secretary Liz Truss said Thursday.

Truss, who was talking to reporters in Sarajevo after meeting her Bosnian counterpart Bisera Turkovic, warned against "offering a compromise or appeasement to Putin".

"It's about digging deep in our own resources and not backsliding... continuing to supply Ukraine with the weapons they need to win and to take back their territorial integrity and their sovereignty," she said.

"We need to make sure that Putin loses in Ukraine and that Ukraine prevails... that Russian aggression is never again allowed to threaten peace in Europe."

Recalling Bosnia's inter-ethnic war in the 1990s that killed nearly 100,000 people, Truss warned against current signs of Russia's interference in the country which, she said, "risk plunging us back into those dark days".

"This must be stopped," she said and pledged Britain's support in preventing it.

Britain is aiming to mobilise $100 million (93 million euros) of UK-backed investment in the Western Balkans by 2025, Truss added.

The Russian invasion of Ukraine in late February increased fears of escalations of tensions in the volatile Balkans, traditionally torn between East and West, and where Russia seeks to boost its influence.

In Bosnia, ethnic Serb leader Milorad Dodik became increasingly vocal about his secessionist aims, widely believed to have the backing of Moscow.

His moves stirred fears that the country could break up or even be plunged into a new conflict.

Dodik was sanctioned by the United States and Britain notably for threatening Bosnia's stability and functionality.

On Thursday, Turkovic said the Balkans and her country were at an "important turning point".

"The crisis in Ukraine may and could be intended to spill over to this part of Europe," the minister warned, stressing the need for Western support for Sarajevo's bid to join the European Union and NATO.

Giving Bosnia an EU candidate status would be a "good message to all those dancing to Russia's tune", Turkovic said, in a reference to Dodik.

Since the 1992-1995 war Bosnia consists of two semi-independent entities -- the Muslim-Croat Federation and the Serbs' Republika Srpska. They share weak central institutions.