The Kremlin says President Vladimir Putin has approved a draft treaty to make Crimea part of Russia.
The move comes shortly after Putin formally informed both houses of parliament of Crimea's request to become part of Russia -- the first legislative step required by the Russian Constitution if the peninsula is to be annexed from Ukraine.
Putin is due to address a joint session of parliament about Crimea at noon CET today.
On March 17, Putin recognized Crimea as an independent state in defiance of the international community's insistence that it remain part of Ukraine.
Putin signed that order just hours after Crimea’s parliament declared independence from Ukraine and formally applied for membership in the Russian Federation.
Also on March 17, the United States and the EU imposed sanctions against Russian officials, Russian weapons firms, and pro-Russian Ukrainians over Moscow's intervention in Ukraine.
President Barack Obama announced the sanctions in Washington.
"[This] series of measures that will continue to increase the cost on Russia and on those responsible for what is happening in Ukraine," Obama said. "First, as authorized by the executive order I signed two weeks ago, we are imposing sanctions on specific individuals responsible for undermining the sovereignty, territorial integrity and government of Ukraine. We're making it clear that there are consequences for their actions."
Obama also threatened additional sanctions if the Kremlin makes what he called “further provocations."
The U.S. sanctions list includes Russian Deputy Prime Minister Dmitry Rogozin; the head of the Federation Council upper house of parliament, Valentina Matviyenko; and two of President Vladimir Putin’s aides – Vladislav Surkov and Sergei Glazyev.
It also includes State Duma lower house deputies Leonid Slutsky and Yelena Mizulina, and Federation Council member Andrei Klishas.
Ukrainians on the U.S. list include ousted President Viktor Yanukovych; the head of the pro-Russian Ukrainian Choice political organization, Viktor Medvedchuk; and two pro-Russian Crimean political leaders -- Sergei Aksyonov, who claims to be Crimean prime minister, and Vladimir Konstantinov, speaker of Crimea’s parliament.
White House spokesman Jay Carney did not rule out that Washington could eventually target Putin with sanctions, or provide U.S. military assistance to Ukraine's new authorities.
But he said the American focus remained on diplomacy and trying to de-escalate the situation.
"Our focus continues to be on supporting economic and diplomatic measures to de-escalate the situation, not escalate it," Carney said.
In Brussels, the EU announced travel bans and asset freezes against 21 people -- 13 Russians and eight Crimeans.
They include Crimean Aksyonov and Konstantinov; Vice Admiral Aleksandr Vitko, commander of Russia's Crimea-based Black Sea fleet; and Russian lawmaker Sergei Mironov, who initiated the State Duma legislation needed to allow Crimea's annexation under Russian constitutional law.
The EU also said it would sign with Ukraine's new authorities the political provisions of an EU Association Agreement on March 21.
This is the same agreement Yanukovych rejected in November, igniting the protests that led to his ouster.
Meanwhile, Japan has also slapped sanctions on Moscow over Ukraine.
Japanese Cabinet Secretary Yoshihide Suga said on March 18 that the government is freezing all talks with Russia on relaxing visa requirements, and on all new negotiations on investment accords and new agreements on space and military activities.
On March 16, pro-Russian authorities in Crimea staged a referendum calling for the region to be annexed by Russia.
Putin says the referendum is legal and Russian lawmakers have drafted legislation to prepare for the annexation of Crimea under Russian constitutional law.
The United States and the European Union have refused to recognize the referendum results, saying the vote violated Ukraine’s constitution.
With reporting by AP, AFP, Itar-Tass