David Cameron has said a G8 summit scheduled to take place in Russia this June cannot go ahead as the EU and US attempt to isolate Moscow over its actions in Ukraine.
Speaking in The Hague ahead of a meeting of G7 leaders he said it was "absolutely clear" the summit could not take place.
He said: "We should be clear there's not going to be a G8 summit this year in Russia. That's absolutely clear."
Mr Cameron warned Vladimir Putin Russia would face further sanctions if forces moved further into Ukraine after reports troops were massing near the border.
David Cameron says the G8 summit in Russia "cannot go ahead"
He said: "These reports are concerning and we need to send a very clear message to the Russian government and to President Putin that it would be completely unacceptable to go further into Ukraine, and that would trigger sanctions from the EU, from the US, from other countries as well."
The G7 meeting is expected to discuss possible responses to Russian actions in Ukraine as well as concerns that Moscow could be looking to extend its control beyond Crimea.
Preparations for the summit in Sochi had already been suspended as a result of Russia's actions in Ukraine.
On Monday, the Ukrainian Defence Ministry was told to pull all its forces from Crime as Russian troops extended their control over the disputed territory.
Monday's seizure came two days after Russian troops stormed the Belbek base
Speaking in parliament, acting president Oleksander Turchinov said the decision was taken in the face of "threats to the lives and health of our service personnel".
He said: "The National Defence and Security Council has instructed the Defence Ministry to carry out a re-deployment of military units in Crimea and carry out the evacuation of their families."
Russian troops, backed by helicopters and armoured personnel carriers, forced their way into the base in Feodosia in the early hours of Monday morning.
President Obama will hold crisis talks with G7 leaders later on Monday
Ukrainian defence ministry spokesman Vladislav Seleznyov said: "The invading troops were using stun grenades and also firing automatic weapons... The interior of the compound is full of Russian troops."
In a statement on his Facebook page, Mr Seleznyov added that paratroopers descended into the base from four helicopters hovering above.
He said three Russian vehicles were then seen leaving the base with Ukrainian marines whose hands had been tied up.
General Breedlove is concerned about the size of Russia's troop build-up
Ukrainian army officer, First Lieutenant Anatoly Mozgovoy, confirmed shots were fired at unarmed Ukrainian soldiers during the seizure, however there are currently no reports of any injuries.
The Feodosia base had been one of the last few military facilities still flying Ukrainian flags after Russia's annexation of Crimea. Those flags have now reportedly been removed.
Speaking in Amsterdam on Monday US President Barack Obama said Europe and the United States are united in their support for the Ukrainian interim government.
There are fears Russian forces are eyeing Ukraine's Transdniestria region
He said both the EU and US were prepared to "impose a cost" on Russia for its actions so far.
Nato's top commander in Europe, General Philip Breedlove, has warned that Russia's military force massing on Ukraine's border was "very, very sizeable and very, very ready".
He said he was worried the Russian military could make a move for Moldova's breakaway Transdniestria region.
Transdniestria, a narrow strip of land to Ukraine's southwest, already has a Russian military presence and most people there favour a union with the country.
Crimea landgrab 'cannot be won back', say experts
Russian President Vladimir Putin last week signed papers making Crimea part of Russia, saying it was complying with international agreements and had no plans to invade.
It has also called the soldiers who took over Ukrainian bases in Crimea "self-defence forces".
On Monday ex-Chief of the General Staff Lord Dannatt said Western "weakness" had allowed Putin to "become bold on his own fringes" and seize the region.
He called for heightened military spending in the UK and as well as tougher sanctions against Russia.
The US and European Union have already targeted some of Mr Putin's closest political and business allies with personal sanctions and have threatened broader economic sanctions if his forces encroach on other parts of Ukraine with large Russian-speaking populations.