WASHINGTON, Nov 26 - US President Donald Trump says he may cancel a meeting with Russian President Vladimir Putin following a maritime clash between Russia and Ukraine, BBC reported on Tuesday.
Trump told the Washington Post he was waiting for a "full report" after Russian ships fired on and seized three Ukrainian boats on Sunday.
The two leaders are due to meet on the sidelines of the G20 summit in Buenos Aires later this week.
Meanwhile, the US has 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.
He told the Washington 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 men are scheduled to discuss security, arms control, and issues in Ukraine and the Middle East when the summit convenes on Friday and Saturday, national security adviser John Bolton told reporters.
Russian coastguard ships opened fire on Sunday as the 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. The court is expected to issue rulings for the remaining servicemen on Wednesday.
The FSB security service has since released videos of some of the men making statements. One of them, Volodymyr Lisovyi, said he was aware of the "provocative nature" of the Ukrainian action.
Another, Andriy Drach, said he had been on a gunboat with an order to sail from Odessa to Mariupol.
"We were warned by the border service of the Russian Federation that we were violating Russian law. They had repeatedly asked us to leave the territorial waters of the Russian Federation," he said.
Ukraine's navy commander, Ihor Voronchenko, told Ukrainian TV that the men had given false statements under duress.
"I know those sailors from Nikopol. They have always been honest professionals in their jobs, and what they say now is not true," he said.
On Monday night, Ukraine's parliament backed President Petro Poroshenko's decision to impose martial law for a 30-day period from 26 November in 10 border regions.
On Tuesday, President Poroshenko said there was a threat of "full-scale war" with Russia.
"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.
The move to martial law is unprecedented in Ukraine, and gives military authorities the right to ban protests and strikes. (bbc/ez)