Both Russians and Crimea's majority ethnic Russian population see annexation as correcting a historic insult.
Russia's President Vladimir Putin on Tuesday approved a draft Bill for the annexation of Crimea, one of a flurry of steps to formally take over the Black Sea peninsula.
Crimea on Sunday voted overwhelmingly to secede from Ukraine and seek to join Russia. The West and Ukraine described the referendum which was announced two weeks ago as illegitimate.
The United States and the European Union on Monday announced asset freezes and other sanctions against Russian and Ukrainian officials involved in the Crimean crisis. President Barack Obama warned that more would come if Russia didn't stop interfering in Ukraine.
Russian troops have been occupying the region for more than two weeks.
The decree signed by Putin and posted on the official government website on Tuesday morning is one of the steps which would formalise the annexation of Crimea. Russia, however, still has a room to back off. The treaty to annex Crimea has to be signed by leaders of Russia and Crimea, approved by the Constitutional Court and then be ratified by the Parliament.
Russia's claim on Crimea
Putin is set to address both houses of the Parliament at 3pm Moscow time (11am GMT) in a nationally televised speech where he is widely expected to stake Russia's claim on Crimea.
Crimea had been part of Russia since the 18th century until former Soviet leader Nikita Khrushchev transferred it to Ukraine in 1954. Both Russians and Crimea's majority ethnic Russian population see annexation as correcting a historic insult.
Ukraine's turmoil, which began in November with a wave of protests against President Viktor Yanukovych and accelerated after he fled to Russia in late February, has become Europe's most severe security crisis in years. – Sapa-AP