Russia on Monday will mark the fifth anniversary of Moscow's annexation of Crimea from Ukraine, condemned by the West but celebrated by most Russians.
President Vladimir Putin will take part in celebrations in the Black Sea peninsula, where he is also due to launch a new power station, the Kremlin said.
Moscow's 2014 takeover of Crimea was denounced by Kiev and the West as an annexation and led to sanctions against Russia, but it resulted in a major boost of Putin's popularity at the time.
In Russia, March 18 has been officially proclaimed as the "Day of Crimea's Reunification with Russia".
In Moscow, city authorities have thrown a street festival called "Crimean Spring" that hosts jazz concerts, cooking workshops and a photography exhibition a stone's throw from the Kremlin.
Up to 10,000 people are expected to take part in a flash mob in the Moscow region Monday, dancing to the Soviet-era song "Waltz of Sevastopol" -- the Crimean city home to Russia's Black Sea fleet.
Hundreds are expected to participate in another flash mob recreating the Russian flag in the Crimean seaside resort Yalta.
"For us, the question of Crimea is decided forever," Russian foreign ministry spokeswoman Maria Zakharova said several days before the anniversary.
"This is because its reunification with Russia was the result of the free will of the peninsula's people in a referendum," she added.
The March 2014 referendum, held by Crimean authorities, was not recognised internationally.
Putin signed a treaty with representatives from Crimea to make it part of Russia two days after the unrecognised vote, on March 18 2014.
Ukraine and much of the international community condemned the move as a violation of international law.
Last week, the United States, Canada and the European Union slapped new sanctions on more than a dozen Russian officials and businesses in response to Moscow's "continued aggression in Ukraine".
But Putin, whose approval ratings soared after Moscow took over Crimea, has repeatedly rejected any prospect of returning the peninsula to Ukraine.
"What, have you gone mad?" he told a journalist who asked him if there were any circumstances under which he would be ready to give up Crimea in a documentary aired last year.
"There are no such circumstances and never will be."
Atmosphere of terror
"All these five years there has been an atmosphere of both open and hidden terror against the people of Crimea and international law," Ukrainian Foreign Minister Pavlo Klimkin told AFP.
The Crimean Tatars, a Muslim-majority community that is largely opposed to the annexation, have faced pressure from Russian authorities.
Russia has banned the Mejlis, the Crimean Tatars' elected assembly which resisted Russian rule, denouncing it as extremist.
"Crimea was taken away from the Crimeans, their homeland was taken away from them," Klimkin said.
Ukraine "feels pain for this every day" and that "the international community will never recognise" the annexation, he said.
But surveys show Russians are less enthusiastic about Crimea being under Moscow's rule than they were five years ago.
According to a survey published by the Center for Public Opinion (FOM) in early March, only 39 percent of Russians believe the annexation brought Russia more good than harm, compared to 67 percent in 2014.