File photos of Ukraine President Volodymyr Zelensky and Russian President Vladimir Putin. Photograph:( AFP )
The comments come shortly after tensions between Kiev and Moscow after Kremlin sent troops to Ukraine's border for military drills.
Ukraine's President Volodymyr Zelenskiy said on Thursday that Russia's issuance of its passports to residents of eastern Ukraine is the first step towards the "annexation" of the region.
"This is definitely the first step, because the same thing happened once in Crimea, Crimea residents were given Russian passports. This is a big problem," Zelenskiy told a news conference.
The comments come shortly after tensions between Kiev and Moscow reached a fever pitch when the Kremlin sent tens of thousands of troops to Ukraine's border to run military drills.
The move exacerbated tensions between the ex-Soviet former allies stemming from Russia's takeover of Crimea and support for separatists that have controlled two regions of eastern Ukraine since 2014.
Zelensky said that Russia was still flexing its muscle on the Black Sea and that it had only removed 3,000 to 3,500 troops from Crimea.
"The forces that remain along the Ukrainian border permit the Russian side to launch a military operation against Ukraine at any moment," Zelensky said.
US Secretary of State Antony Blinken raised Washington's "deep concerns" about Russian troops amassed along the Ukraine border despite an announced pullback, in his first talks with his Russian counterpart Sergei Lavrov on Wednesday.