President Vladimir Putin has defended the seizure of three Ukrainian ships last weekend, but President Donald Trump has expressed “deep concern” at Moscow’s actions against a US ally.

Putin said the Ukrainian ships entered Russian territorial waters and refused to respond to requests to stop from Russian patrol boats.

The captured Ukrainian sailors have been put before a court in Simferopol to be held in pre-trial detention for two months.

Trump threatened to cancel planned talks with Putin at this week's G20 summit on Tuesday following the incident.