The EU froze ousted President Viktor Yanukovych’s assets in Europe, as well as targeting 18 people close to him.
European leaders also suspended visa talks with Russia and unveiled an €11bn (£9.1bn) finance package on offer to Ukraine’s government.
David Cameron said travel bans in Europe are also an option.
But tensions in the Crimea continued to rise – the region’s parliamentarians voted to secede from the country and join Russia.
The local government also said it intends to hold a referendum in just 10 days time to determine whether or not Crimea will remain a part of Ukraine. The move was condemned as “illegal” by the US and EU, who are calling for Russian troops to pull out of the country.
“We call on Russia to immediately withdraw its armed forces and allow immediate access for international monitors,” said European Council head Herman Van Rompuy.
“We consider the decision by Crimea’s Supreme Council to hold a referendum as contrary to the Ukrainian constitution and therefore illegal.”
There are also questions over how fair a vote could be when troops are occupying the region.