Foreign Secretary Boris Johnson is to become the first British Foreign Secretary to visit Moscow in more than five years.

The Foreign Office announced he has accepted an invitation to visit the country in the next few weeks.

Foreign Office sources have been keen to stress the visit does not signal a step change in diplomatic relations with Russia, which have become increasingly strained in recent years, particularly since the polonium poisoning of British citizen and former Russian agent Alexander Litvinenko at a London hotel in 2006.

An unnamed Foreign Office source told the BBC: "He is not going in order to reset the relationship. He has been clear in his calls with Lavrov that this can't happen till they change course on issues such as Ukraine.

"He intends to say the same things face to face as we do in public and in Parliament about Russian activities. While it may be a tough visit, that is what needs to be done.

"Boris has always said we must engage when in our interests. He calls it 'guarded engagement'. He will be robust in the meetings and defend our position. This is not about cosying up, in fact quite the opposite."