The United States believes that Russian President Vladimir Putin's threatened retaliation against Ukraine over its drone attack last weekend has not happened yet in earnest and is likely to be a significant,

(Reuters) -Overnight missile and bomb strikes by Russia on the Ukrainian city of Kharkiv left three people dead and 22 hurt, while a Ukrainian drone attack in the Moscow region wounded two people, officials from both countries said separately on Saturday.

President Trump said the Russian leader Vladimir Putin had warned that he would retaliate for a covert Ukrainian attack in Russia last weekend that destroyed dozens of Russian bombers.