Western countries denounced the Russian incursion, launched as the U.N. Security Council was debating the prospect of intervention, and pledged to introduce tough punitive measures on the Kremlin.

It was not immediately clear whether Moscow's forces had formally moved into the parts of Ukraine’s Donetsk and Luhansk region controlled by separatists – most analysts and Ukrainian officials have said that some Russian forces have long been informally established inside them.

The moves, announced after a meeting of Russia’s Security Council and a rambling, impassioned address by Putin to Russians, were not the full-fledged invasion predicted by many in the West after weeks of deployment by Russian troops on Ukraine’s borders.

The country's partners have already pledged over $5 billion in financial aid in a move to support Ukraine's economy and reform agenda.

Some Western leaders have in the past week warned of an imminent Russian invasion, with U.S. President Joe Biden saying he was “convinced” this would occur within days and Secretary of State Antony Blinken predicting a quick advance aimed at capturing the Ukrainian capital, Kyiv.

The proposed summit was announced in Washington and Paris hours after the United States issued a fresh warning that Russian forces were poised for an attack on Ukraine within days.