At summit on Crimea, Russia warned against new annexations in Ukraine

Western leaders have warned Russia against annexing other parts of Ukrainian territory after Crimea amid rumours Russia is planning to do so in various occupied areas.

The leaders sent video addresses to the Crimea Platform conference in Kiev on Tuesday which was attended in person by Ukrainian President Volodymyr Zelenskyy and his Polish counterpart Andrzej Duda.

The Crimean peninsula was seized and illegally annexed by Russia in 2014, after a referendum widely deemed illegitimate.

Duda said the West's muted reaction to the annexation constituted "appeasement" of Russia, adding there could be no more "business as usual" in the West's relations with Moscow.

The 2014 annexation of Crimea led to a "clear deterioration of the humanitarian situation and of human rights in the peninsula," said French President Emmanuel Macron, who vowed EU support to Ukraine "for the long term".

Since February, Moscow has been using Crimea as a staging post for attacks on Ukraine as well as "a testing ground for the brutal methods Russia is now applying across the other occupied parts of Ukraine," European Commission President Ursula von der Leyen told the conference.

Turkish President Recep Tayyip Erdogan said Türkiye supports Ukraine's territorial integrity and rejects the illegal annexation of Crimea.

"The return of Crimea to Ukraine, of which it is an inseparable part, is essentially a requirement of international law," Erdogan said.

British Prime Minister Boris Johnson accused Russian President Vladimir Putin of "planning more annexations and more sham referendums", saying it has never been more important to stand together".

READ MORE: Erdogan: Return of Crimea to Ukraine a requirement under international law

Fighting continues

As tensions grew in the capital, the US embassy in Kiev issued a security alert and reiterated its appeal for US nationals to leave Ukraine.

"The Department of State has information that Russia is stepping up efforts to launch strikes against Ukraine's civilian infrastructure and government facilities in the coming days," it said.

Ukrainian President Zelenskyy and other officials also warned that Russia could step up attacks around the Independence Day holiday.

Ukraine's Western allies have supplied Kiev with billions of dollars of military equipment and imposed ever more stringent sanctions on Russia.

Moscow has accused Western powers of escalating the conflict with its support for Ukraine.

READ MORE: 'Almost 9,000' Ukrainian military personnel killed in conflict with Russia