US President Donald Trump says he has cancelled an upcoming meeting with Russian President Vladimir Putin because of the Russia-Ukraine standoff.

Taking to Twitter on Thursday, Trump said his decision to cancel the meeting with Putin at the G20 summit in Buenos Aires, Argentina, was based on the fact that the Ukrainian ships and sailors seized by Russia on Sunday have not been returned.

"I have decided it would be best for all parties concerned to cancel my previously scheduled meeting... I look forward to a meaningful Summit again soon as this situation is resolved", he wrote.

Russia on Sunday seized two small Ukrainian armoured artillery vessels, a tugboat and some 23 crewmembers, which it said had illegally entered its territorial waters.

The vessels were approaching the Kerch Strait when the tugboat was struck, damaging its engine, guardrail and outer shell.

Following the incident, Ukraine's Navy said Russia had "once again demonstrated its aggressive nature and complete neglect of the norms of international law."

The following day, Ukraine's parliament voted to introduce martial law for 30 days in areas of the country deemed most vulnerable to an attack from Russia.

READ: Ukraine - what is meant by martial law?

NATO called for calm following the incident, while the European Union urged Kyiv and Moscow to “act with utmost restraint to de-escalate” tensions in the Black Sea.

Speaking at a financial forum in Moscow on Wednesday, Putin said the Ukrainian vessels had clearly been in the wrong, as he accused Poroshenko of orchestrating the crisis to boost his ratings ahead of elections next year.

“It was, without doubt, a provocation,” he said.

“It was organised by the president ahead of the elections. The president is in fifth place ratings-wise and therefore had to do something. It was used as a pretext to introduce martial law.”

Euronews has reached out to Putin's office for comment on Trump's decision to cancel the meeting.