The UK government has said it will sanction Russia over President Vladimir Putin's decision to recognise two breakaway regions in eastern Ukraine.
Recent legislation will be used to impose restrictions on people and organisations linked to Russia, the BBC understands.
Government sources say sanctions would be "ratcheted up" in the event of a Russian incursion of Ukraine.
The foreign secretary said Russia's actions would not go "unpunished".
Liz Truss
confirmed sanctions would be announced on Tuesday "in response to their breach of international law and attack on Ukraine's sovereignty and territorial integrity".
Several of the UK's western allies, the US, France and the European Union, made similar statements, condemning Mr Putin's move and promising sanctions.
Prime Minister Boris Johnson will chair a Cobra emergency response meeting at 06:30 GMT on Tuesday.