Russian President Vladimir Putin has informed parliament formally of Crimea's request to join the country, the first legislative step towards absorbing the peninsula.
Mr Putin, who officially recognised Crimean independence on Monday, also approved a draft bill on the accession.
Crimean officials say 97% of voters backed splitting from Ukraine in Sunday's controversial referendum.
The EU and US have declared the vote illegal and imposed sanctions.
Travel bans and asset freezes have been imposed on government officials and other figures in Russia, Crimea and Ukraine.
France's Foreign Minister Laurent Fabius said Paris had cancelled planned ministerial defence and foreign relations talks due to take place in Moscow on Tuesday, saying they would have been "ill-timed".
Ukraine's foreign ministry, meanwhile, has issued a "decisive and categorical protest" against Russia's actions, saying they fell short of Russia's international commitments.
In a bid to encourage loyalty among Ukraine's other mainly Russian-speaking regions in the east and west, Ukraine's interim Prime Minister Arseniy Yatsenyuk said on Tuesday that Kiev was prepared to grant them "the broadest range of powers".
In a pre-recorded address on Ukraine's 5 Kanal TV - delivered in Russian - Mr Yatsenyuk said the reforms would give cities the right to run their own police forces and make decisions about education and culture.
The peninsula was taken over by pro-Russian forces in late February after Ukraine's pro-Moscow President Viktor Yanukovych fled to Russia following months of protests, though Russia has always insisted the troops are not under its direct control.
Kiev is also concerned about a build-up of Russian troops on its eastern borders, and has authorised the partial mobilisation of 40,000 troops.
Mr Putin is addressing a special session of Russia's two houses of parliament at St George's Hall at the Kremlin. A delegation of Crimea's new leaders is also there.
Russian news website Gazeta.ru, quoting sources, says that after the speech, President Putin and the speaker of the Crimean parliament, Vladimir Konstantinov, are expected to sign an agreement on Crimea's "entry into the Russian Federation".
Having approved the draft bill, Mr Putin has told MPs "to consider it practical to sign the agreement at the highest level," Russia's Interfax news agency reports.
Once signed, the bill must be approved by the constitutional court and then ratified by parliament.
The process is likely to be completed this week, after which Crimea is expected to be considered a new part of the Russian Federation, with the status of a republic.
Moldovan President Nicolae Timofti said any Russian moves to accept Trans-Dniester "would be a step in the wrong direction".
Crimea was transferred from Russia to Ukraine while under Soviet rule in 1954 and much of its population is ethnic Russian.
The results of Sunday's referendum were celebrated by many Crimeans, but the vote was widely criticised by Western leaders and at the UN.
Voters had been asked to choose between joining Russia or having greater autonomy within Ukraine. There was no option for those who wanted the constitutional arrangements to remain unchanged.
Many among Crimea's ethnic Ukrainians and Tatars - together making up about a third of the population - had said they would boycott the vote.
The Tatars were driven from Crimea under the Soviet Union, only being able to return after the collapse of the USSR. They have expressed fears of persecution under Russia.
On Monday, the EU and US published separate lists of sanctions in response to Moscow's intervention. Both included Crimea's acting leader, Sergei Aksyonov, and speaker Mr Konstantinov.
But the BBC's Richard Galpin in Moscow says the sanctions have largely been dismissed in Russia, including by those they targeted.
Yuri Ushakov, Mr Putin's senior foreign policy adviser, told Russian media the measures "provoke only feelings of irony and sarcasm".
Despite the condemnation, Mr Putin seems intent on pushing ahead very quickly with the annexation of Crimea, our correspondent adds.