US President Donald Trump on Thursday scrapped a planned meeting at the G20 summit with his Russian counterpart Vladimir Putin over Moscow's detention of a group of Ukrainian sailors.

“Based on the fact that the ships and sailors have not been returned to Ukraine from Russia, I have decided it would be best for all parties concerned to cancel my previously scheduled meeting in Argentina with President Vladimir Putin,” he wrote on Twitter.

“I look forward to a meaningful Summit again as soon as this situation is resolved!,” Trump added, shortly after taking off for the weekend summit in Buenos Aires.

Putin has insisted that Russian forces were in the right to seize three Ukrainian ships last weekend, however, President Trump has expressed “deep concern” at Moscow's actions against a US ally.

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

Moreover, Ukraine’s president signed an act imposing martial law in border regions on Wednesday. President Petro Poroshenko’s spokesman confirmed he had signed the act, which introduces martial law for 30 days in 10 regions bordering Russia, the Black Sea and the Azov Sea.