US President Donald Trump says he may cancel a meeting with Russian President Vladimir Putin following a maritime clash between Russia and Ukraine.
Mr 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 Mr 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.