At least three explosions have been heard in the Ukrainian capital Kyiv, after air raid sirens went off.
Ukraine's Nato-led allies have announced deliveries of advanced air defence weapons to Kyiv, after a spate of Russian missile strikes.
President Zelensky has urged countries to hit Russia with more sanctions in response to "a new wave of terror" after Monday's attacks on Ukraine.
Russia has been widely condemned after bombarding cities across Ukraine, including launching missile strikes on the centre of Kyiv for the first time.
A large fire on the only crossing between the occupied Crimean peninsula and Russia was caused by a lorry explosion, Russian officials say.
Russia's President Vladimir Putin has signed the final papers to annex four regions of Ukraine - even as his military suffered further setbacks.
Ukrainian forces have liberated a key village in the southern region of Kherson, hastening another Russian military retreat.
This week, one Russian newspaper, Moskovsky Komsomolets, concluded: "Vladimir Putin has nowhere to retreat. So, he'll continue to attack."
European countries say they will ramp up security around oil and gas installations after the suspected sabotage of two major pipelines.
The Bank of England has said it will step in to calm markets after the government's tax-cutting plans sparked a fall in the pound and caused borrowing costs to surge.
Russia's unmanned Luna-25 spacecraft has crashed into the Moon after spinning out of control, officials say.
Donald Trump has confirmed that he will not take part in Republican presidential debates with his rivals in the race for the White House.