German Foreign Minister Annalena Baerbock said Monday delaying European Union accession for the countries of the Western Balkans risked leaving them open to Russian "infiltration".

"Taking the six states in the region under our wing on their way into the European Union has become a geopolitical necessity in light of Russia's brutal imperialism," Baerbock said in a statement.

"We cannot allow any grey areas in Europe and together we must do everything we can to protect the flanks that Russia can use for destabilisation, disinformation and infiltration," she said ahead of a visit to the Western Balkans.

Support for the countries of the region could include "strengthening their democratic institutions, improving their resilience and offering their people economic prospects", she said.

Baerbock was headed to Montenegro on Monday before travelling on to Bosnia and Herzegovina.

The war in Ukraine has reignited the EU's drive to expand into central and eastern Europe.

In December 2022, Bosnia became the fifth Balkan nation to be given candidate status, following North Macedonia, Montenegro, Serbia and Albania.

Kosovo also applied in 2022 but has yet to be given candidate status.

But frustrations have grown across the Balkans at the slow pace of negotiations with the EU over potential membership.

The bloc has vowed to help double the economy of the Western Balkans over the next 10 years, opening up part of the European single market to the region.

Baerbock said Montenegro had put forward an "ambitious agenda" to advance towards EU membership.

Key areas remained improving the "rule of law and the fight against corruption", Baerbock said.

Bosnia, meanwhile, stood at a "crossroads" after the EU gave it candidate status, and would similarly have to pursue reforms, she said.

Germany opposed "those who put obstacles in Bosnia and Herzegovina's path to the EU with their fantasies of division", Baerbock said.

Russia has maintained a close relationship with Bosnian Serb leader Milorad Dodik.

Dodik, who received one of Russia's highest honours from President Vladimir Putin last month, has challenged Bosnia's post-war ruling structure over the past several months.