Belarus said on Monday that a group of people damaged the facade of its embassy in London and physically attacked some of its diplomats, badly hurting one of them in an incident on Sunday evening.
One of the diplomats was treated for a broken nose, light concussion and a broken tooth, the Belarusian Foreign Ministry said in a statement on its website.
The assailants tried to hide, but some of them were detained and they are thought to belong to a radical emigre group called "Nadzeya," it said.
A Facebook group with the same name appeared to support members of the Belarusian political opposition that was crushed in a crackdown on mass anti-government protests last year.
The Belarusian ministry said it had called in a British diplomat to protest over the incident and to demand a full investigation.