G20: Trump may cancel Putin talks over Ukraine

US President Donald Trump has said he may cancel a meeting with his Russian counterpart Vladimir Putin following a maritime clash between Russia and Ukraine.

Trump told the Washington Post he was waiting for a "full report" after Russian ships fired on and seized three Ukrainian boats on Sunday. A Crimean court was expected to decide the fate of detained Ukrainians on Wednesday, the BBC reported.

The US President has told the Post that the report coming from his national security team would be "very determinative". "Maybe I won't have the meeting (with Putin). Maybe I won't even have the meeting. I don't like that aggression. I don't want that aggression at all," he said.

The two leaders were due to meet on the sidelines of the G20 summit in Buenos Aires later this week and discuss security, arms control, and issues in Ukraine and the Middle East after the meet convenes on Friday, national security adviser John Bolton told reporters.

The US has also urged European states to do more to support Ukraine.

State department spokeswoman Heather Nauert said Washington wanted to see tougher enforcement of sanctions against Russia.

Russian coastguard ships opened fire on Sunday as two Ukrainian gunboats and a tug sailed through the Kerch Strait off the coast of Crimea, which was annexed by Russia in 2014.

Twenty-four Ukrainians were detained and at least three were wounded in the incident.

Ukraine described it as an "act of aggression" but Russia said the ships had illegally entered its waters.

A Crimean court later ordered that 12 of the Ukrainians be detained for 60 days.

On Tuesday, Ukrainian President Petro Poroshenko said there was a threat of "full-scale war" with Russia, a day after Kiev imposed martial law for a 30-day period from November 26 in 10 border regions, the BBC reported.

"The number of (Russian) tanks at bases located along our border has grown three times," he said.

Five of the 10 regions border Russia while two are adjacent to Moldova's breakaway Trans-Dniester region, where Russian troops are stationed. The other three regions border the Black Sea or Sea of Azov close to Crimea.