Crimea, which seceded from Ukraine, signed a treaty on the autonomous region joining Russia.
Russian President Vladimir Putin and Crimea's Prime Minister Sergei Aksyonov on Tuesday signed the bill to make the Black Sea peninsula a part of Russia.
The bill of accession has to be approved by Russia's Constitutional Court and then ratified by the parliament to become legally valid.
Earlier, addressing a joint session of both the houses of Russian parliament, President Putin staunchly defended Moscow's actions and Crimean referendum, saying that "Crimea has always been part of Russia."
He called on the lawmakers, who frequently applauded during Putin's speech, to approve the bill for Crimea becoming part of the Russian federation.
However, Putin made it clear that Russia does not want a break-up of Ukraine.
The day began with Russia's iron man recognizing Crimea as a sovereign Russian state and approving a draft bill on the accession.
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