U.S. President Barack Obama on Tuesday hit out at Moscow's expansionism as a "sign of weakness" after Russia took control of the Crimean peninsula from Ukraine, fueling fears of further intervention in the region.

"Russia is a regional power that is threatening some of its immediate neighbors, not out of strength but out of weakness," Obama told journalists after a nuclear security summit in The Hague.

The U.N. General Assembly is to vote Thursday on a resolution submitted by Ukraine denouncing the referendum in Crimea and the region's annexation by Russia -- but without explicitly criticizing Moscow.

The text is similar to the one submitted to the Security Council on March 19, but which was blocked by Russia's veto.

Crimea's firefighters proudly switched allegiance on Tuesday, becoming the disputed peninsula's first department under Russia's full control after a hastily arranged ceremony reminiscent of the Soviet era.

"Lutsevich! Where is Lutsevich?!" echoed the booming voice of the Black Sea peninsula's emergency services deputy chief, Andrei Tkachenko.

Russia on Tuesday confirmed a young female lawyer who has won a huge Internet following for her attractive looks, especially in Japan, as prosecutor for Crimea after Moscow incorporated the region into its territory from Ukraine.

Natalya Poklonskaya, 34, has become a web sensation around the world for her good looks and soft voice during the crisis between Russia and Ukraine over the Black Sea peninsula.

Ukraine's former prime minister Yulia Tymoshenko was plunged into fresh controversy on Tuesday after Russian television broadcast a tape where she is heard urging the "wiping out" of Russians over Moscow's seizure of Crimea.

Tymoshenko, a hugely controversial figure both in Ukraine and Russia who was released from jail last month, confirmed the voice was hers but said some of the comments had been manipulated.

One of Russia's most prestigious universities faced accusations Tuesday of "political censorship" after it sacked a prominent professor for comparing Russia's takeover of Crimea to Nazi Germany's annexation of Austria.

The Moscow State Institute of International Affairs (MGIMO), which is run by the Russian foreign ministry, on Monday said it had dismissed philosophy professor Andrei Zubov for his public criticism of Russia's actions in Ukraine's Crimea region.

Russia on Tuesday dismissed as counterproductive the decision of G8 member countries to snub a June summit in the Russian resort of Sochi following Moscow's annexation of Crimea.

A summit of the smaller Group of Seven agreed in The Hague on Monday to deepen Moscow's isolation over the crisis in Ukraine and meet without Russia in Brussels instead of gathering in Sochi.

Japan is to give up to $1.5 billion in financial aid to Ukraine, the government in Tokyo confirmed Tuesday, as the club of rich nations booted Russia off the membership list.

Prime Minister Shinzo Abe announced the figure as he and fellow world leaders, including U.S. President Barack Obama, cancelled an upcoming G8 meeting in Sochi, and said it would be replaced by a G7 event that did not involve Moscow.

The G7 group of top economic powers on Monday scrapped a planned meeting to be hosted by Russia as they sought to deepen Moscow's isolation over the Ukraine crisis.

After emergency talks on the Ukraine crisis called by U.S. President Barack Obama, the G7 said they would hold a meeting in Brussels without Russia instead of the wider G8 summit that was to have taken place in Sochi.

Just a year ago, Ruslan, a marine in Ukraine's top battalion stationed in the Crimean port of Feodosiya, helped Russian soldiers paint their armored personnel carrier for a military parade.

On Monday, he spotted the same vehicle being used to block the gate to his base as Russians showered its barracks with tear gas and stun grenades in a pre-dawn raid that took the unarmed Ukrainians by complete surprise.