The Security Council will hold an emergency meeting on Monday after Russia confirmed it had seized three Ukrainian naval ships by force in a strait near Moscow-annexed Crimea, U.S. ambassador to the U.N. Nikki Haley said.

People in Russian-backed areas of eastern Ukraine re-elected separatist leaders at the weekend, according to results released Monday of polls condemned as illegal by Kiev and Western countries.

EU President Donald Tusk fired off an angry broadside at the Kremlin Friday, urging European vigilance and condemning "Russia's aggression" in Ukraine after five soldiers were killed there.

Fighting subsided around a flashpoint Ukrainian town on Sunday following a week-long surge in violence that prompted U.S. President Donald Trump to pledge to help bring peace to Europe's backyard.

The UN Security Council Tuesday called for an immediate return to a ceasefire in Ukraine where three days of fighting in a flashpoint town have left at least 13 dead and thousands of locals without power in freezing conditions.

Ukraine has filed a case at the U.N.'s top court accusing Russia of sponsoring "terrorism" and demanding Moscow pay damages for the shelling of civilians and the downing of flight MH17, officials said Tuesday.

The Organization for Security and Co-operation in Europe, which has been monitoring the pro-Russian insurgency in eastern Ukraine, said Wednesday it was displeased with the "status quo" in the 32-month conflict.

The European Union on Monday extended for another six months damaging economic sanctions against Russia over its intervention in Ukraine.

Ukrainian President Petro Poroshenko urged people not to panic Monday after his government nationalized the country's largest private bank to try and avoid a financial meltdown.

Ukraine ratcheted up tensions with Moscow on Wednesday by warning the Kremlin its army intended to hold two days of missile-launching exercises near the border with Russian-annexed Crimea.