The European Union (EU) has slapped sanctions on another 12 individuals over Russia’s annexation of Crimea from Ukraine.
European Council President Herman Van Rompuy said any further steps by Russia to destabilise Ukraine would have “far-reaching consequences”.
It comes hours after President Barack Obama announced further US sanctions against Russia over the Crimea crisis.
Crimea is in the process of being absorbed into Russia following a disputed referendum in the peninsula.
The referendum has been described as illegal by Kiev and the West.
A treaty joining Crimea to Russia has now been approved by Russia’s lower house of parliament – the Duma – and is expected to be ratified by the upper house on Friday.
For its part, the EU is due to sign the economic sections of a trade pact with Ukraine on Friday. When ousted Ukrainian President Viktor Yanukovych declined to sign it in November, it sparked the current crisis.
Earlier this week, the EU announced asset freezes and travel bans against 21 individuals in Russia and Ukraine.
At the same time the US ordered similar sanctions against 11 individuals.
Washington’s latest measures target a further 20 people closely associated with Russian President Vladimir Putin, as well as a bank, Rossiya, controlled by his allies.
In response, Russia said it was imposing its own sanctions against US officials and politicians.
Following a summit of EU leaders in Brussels on Thursday evening, Mr Van Rompuy said they would also ask the European Commission to prepare for broader economic sanctions against Russia if the crisis escalates.
He described Russia’s annexation of Crimea as “a clear violation of Ukrainian sovereignty and of international law”.
“We strongly condemn the unconstitutional referendum in Crimea. We will not recognise the annexation, nor will we recognise it in the future,” he said.
“There is no place for the use of force and coercion to change borders on the European continent in the 21st Century.”
Mr Van Rompuy said that the 28-nation bloc was also cancelling an EU-Russia summit in June and member states would cancel regular bilateral summits.
“We make clear that failure to settle the crisis peacefully, and any steps by Russia to destabilise Ukraine, will have far-reaching consequences – and by that we mean consequences on relations in a broad range of economic areas,” he added.
The names of the latest individuals to be targeted by the EU will be made public on Friday.
Meanwhile, Moscow has been tightening its grip on Crimea.
On Thursday, Russian-allied troops took over at least two Ukrainian navy ships at anchor in the port of Sevastopol.
A Ukrainian defence ministry spokesman said at least 15 men were involved in the assault.
Pro-Russian forces effectively took over Crimea – with its predominantly ethnic Russian population – after Ukraine’s pro-Moscow President Yanukovych fled Kiev on 22 February following protests in which more than 80 people were killed.