Russian President Vladimir Putin has accused Ukraine of not wanting a peaceful solution to its conflict with Russia.

At a press conference at the end of the G20 summit in Buenos Aires on Saturday, Putin repeated his assertion that the latest incident in the Kerch Strait was a "provocation" by Ukraine which reflected Kiev's attitude.

The ruling party in Kiev was a "party of war" and "as long as it's in power, tragedies of this type and the war will continue," Putin argued, adding that it was always blaming Russian aggression for its leadership failures.

Putin has previously suggested that Ukrainian President Petro Poroshenko engineered Sunday's incident in a bid to improve his chances ahead of next year's presidential election, without providing any evidence for the claim.

On Sunday, Russia seized three Ukrainian naval vessels off the Crimean Peninsula, a territory it annexed from Ukraine four years ago.

In the most dangerous flare-up of violence since 2014, the Russian coastguard opened fire and captured the Ukrainian vessels in the Kerch Strait, which links the Sea of Azov and the Black Sea.

Kiev then instituted 30 days of martial law and imposed border controls on Russian men aged between 16 and 60, citing fears that Russia would infiltrate its territory to stage an uprising.

US President Donald Trump called off a planned meeting with Putin at the G20 over the incident but held "informal conversations" with the Russian leader on the sidelines of the summit, White House spokeswoman Sarah Sanders confirmed Saturday.

Putin said neither he nor Trump had changed their opinion on the situation.

"I answered his question about the incident in the Black Sea in two words," Putin told reporters, expressing regret that Trump had called off their meeting.

"I think the time is ripe for it," he said, saying that the two leaders should discuss the recent US decision to pull out of a decades-old nuclear arms control treaty.

Meanwhile, the government in Kiev said around 100 Russian men had been denied entry to Ukraine in the first 24 hours of the border controls.

There were various reasons for the entry denials, said a spokesman of the border patrol on Saturday.

Some of those denied entry did not provide clear reasons for their trip. Others were only carrying Russian identity documents, as opposed to proper passports.

Russia for its part blocked 40 Ukrainians from entering its territory.