Foreign Secretary Liz Truss will chair an emergency COBRA meeting over the mounting Ukraine crisis.
Ms Truss will lead crunch talks on the growing threat from Russia after British nationals were ordered to leave Ukraine last week.
Boris Johnson will cut short a planned visit to Cumbria to return to London this afternoon in light of the growing threat.
He is expected to chair a full COBR meeting on Tuesday.
A No 10 spokesperson said: "This afternoon the Foreign Secretary will chair a COBR meeting to discuss the consular response to the crisis in Ukraine following Friday's update to travel advice.
“The Prime Minister will receive a security briefing from his intelligence chiefs today.
“Tomorrow the Prime Minister will chair a full meeting of COBR to discuss the UK's response to the current situation.”
The PM's official spokesman warned there was "a grave possibility of an invasion this week" and suggested Parliament could be recalled to in the event of an invasion.
The spokesman said: “In that situation you would expect the Prime Minister would want Parliament to be updated and to have its say."
Mr Johnson travelled to Scotland on Monday morning as part of efforts to tout his levelling up agenda.
But his plans for a series of visits have now been curtailed by the growing crisis.
US intelligence has suggested Russia could launch an invasion as soon as Wednesday, with an estimated 130,000 troops amassed on the border of Ukraine.
On a visit to Rosyth shipyard, the PM warned an invasion of Ukraine could come in the next 48 hours and urged Russian President Vladimir Putin to step back from the "edge of a precipice".
He said: "The signs, as you've heard from (US) President (Joe) Biden that they're at least planning for something that could take place as early as in the next 48 hours.
"That is extremely concerning."
The PM added: "This is a very, very dangerous, difficult situation, we are on the edge of a precipice but there is still time for President Putin to step back."
Downing Street said there were no plans currently for further talks with President Putin but the UK was mounting a diplomatic push to avert war.
Asked if he would would be travelling to Moscow, the PM said: "I'm going to be doing everything I can to help the diplomatic process. I'll be talking to various leaders, including Joe Biden, very soon."
But he insisted that Ukraine's future membership of Nato - which has enraged Russia - could not be "bargained away".
Mr Johnson told reporters: "I think it's very important that we have a conversation, but what we can't do is trade away the sovereign rights of the Ukrainians who aspire to Nato membership.
"That's something that was a massive gain for our world. If you remember what happened in 1990, you had a Europe whole and free, countries could decide their own futures. We can't bargain that away. It's for the Ukrainian people."
Defence Secretary Ben Wallace cut short his family holiday at the weekend to deal with the crisis and he is expected to travel to Brussels this week for Nato talks.
Mr Johnson is expected to make a European trip later this week, but details have not yet been confirmed.
