UK Prime Minister Boris Johnson says the "evidence is pretty clear" that Russia is planning an invasion of Ukraine.

On a visit to Scotland he says there are troops massing on the Ukrainian border and "all sorts of other signs that show that there are serious preparations" going on.

He says this is a "a very, very dangerous, difficult situation" but "there is still time for President (Vladimir) Putin to step back".

He is calling for more dialogue and urges Russia to avoid a "disastrous" invasion.

Russia denies plans to invade Ukraine, despite massing 100,000 soldiers on Ukraine's borders and a reported 30,000 close to the Belarus-Ukraine border.

More than a dozen countries, including the UK and the US, have urged their citizens to leave Ukraine amid warnings of an "imminent" invasion.

Russia wants assurances Ukraine will never be allowed to join Nato - but the alliance's members have opposed this.