Crimea's referendum on joining Russia is "illegal and illegitimate", the European Union said Sunday, announcing that it would decide on sanctions on Monday.

"The referendum is illegal and illegitimate and its outcome will not be recognised," the European Council and European Commission presidents said in a joint statement.

EU foreign ministers meeting from 0830 GMT on Monday "will evaluate the situation tomorrow in Brussels and decide on additional measures" against Moscow, Herman Van Rompuy and Jose Manuel Barroso said.

Crimeans voted Sunday in the referendum on joining Kremlin rule amid intense Western pressure on Moscow not to annex the region in the worst East-West standoff since the Cold War.

Both Washington and Brussels have imposed initial sanctions and warned they will take much more serious steps, up to full economic measures, if the vote went ahead.

The ambassadors of the 28 EU member states were to meet later Sunday to draft a list of Russian and pro-Kremlin Ukrainian officials that could be targeted by sanctions, a diplomat said here.

"We reiterate the strong condemnation of the unprovoked violation of Ukraine's sovereignty and territorial integrity and call on Russia to withdraw its armed forces to their pre-crisis numbers," the EU statement said.