Germany has expelled a "significant number" of Russian diplomats in what Foreign Minister Annalena Baerbock called a response to the "unbelievable brutality" the Kremlin had unleashed in Ukraine.

According to the Agence France-Presse (AFP) report published late Monday, the move involves 40 envoys and follows similar moves by European partners in recent days as a reaction to Russia's war on its neighbor.

"The images from Bucha speak to unbelievable brutality by the Russian leadership and by those who follow its propaganda with a boundless will to exterminate," Baerbock said, referring to the town near Kyiv where dozens of bodies were found in mass graves or littering the streets.

The Kremlin has rejected Western accusations that Russian forces were responsible.

However, Baerbock also said that "similar images" were to be feared "in other places that Russian troops have occupied."

She said it was essential to "stand up for our freedom and be prepared to defend it."

"That is why the German government has decided to declare a significant number of staff of the Russian embassy, who have worked every day here in Germany against our freedom, against the cohesion of our society, as persona non grata," she added.

Baerbock described the diplomats' presence "as a threat" to the more than 300,000 Ukrainians "who have sought protection here" since the invasion began.

"We will no longer tolerate that – we communicated that to the Russian ambassador this afternoon," she said.

Ms Baerbock said Germany would take further steps "with our partners" including "imposing harsher sanctions on Russia, decisively expanding support for Ukraine's fighting forces and bolstering NATO's eastern flank."