Moody's said on Friday it has put the credit ratings of Russia and Ukraine on review for a downgrade after Moscow invaded the neighboring country in what is the biggest attack on a European state since World War Two.

The invasion triggered sanctions from the United States and its European allies against some of Russia’s top banks, military exports and members of President Vladimir Putin's inner circle.

There are "serious concerns" around Russia's ability to manage the disruptive impact of new sanctions on its economy, public finances and financial system, the ratings agency said.

Russia currently has an investment grade rating of Baa3 and a downgrade will lower its rating to junk status.

Ukraine has a B3 rating and Moody's said an extensive conflict could pose a risk to the government's liquidity and external positions, given the country's sizeable external maturities in the coming years and the reliance of its economy on foreign-currency funding.