Ukraine's president signed an act imposing martial law in border regions on Wednesday as mounting tensions over Russia's seizure of Ukrainian ships saw US President Donald Trump threaten to cancel talks with Vladimir Putin.
President Petro Poroshenko's spokesman confirmed he had signed the act, which introduces martial law for 30 days in 10 regions bordering Russia, the Black Sea and the Azov Sea, reports AFP.
The move came after Poroshenko warned of a build-up of Russian forces near Ukraine's borders, escalating the most dangerous crisis in years between the ex-Soviet neighbours.
Western governments have accused Russia of acting illegally in seizing the three ships and Trump has said he is considering cancelling planned talks with Putin at this week's G20 summit in Buenos Aires. Trump said he would make a final decision after hearing a report from national security advisors on this weekend's incident.
"That will be very determinative," Trump told the Washington Post. "Maybe I won't have the meeting."
Russian border patrol boats fired on, boarded and seized the three Ukrainian vessels, along with 24 sailors, on Sunday off the coast of Crimea. The Ukrainian vessels -- a tug and two gunboats -- were trying to pass through the Kerch Strait from the Black Sea to the Azov Sea, but were refused access and chased into international waters by 10 Russian vessels.