Ukrainian officials on Friday upped the ante in the growing confrontation with Russia, announcing a travel ban for most Russian males and searching the home of an influential cleric of the Russian Orthodox Church.

Petro Tsygykal, chief of the Ukrainian Border Guard Service, announced at a security meeting on Friday that Russian males between 16 and 60 will be barred from travelling to the country while martial law is in place.

Ukraine's president, Petro Poroshenko, told the meeting that the measures were taken "in order to prevent the Russian Federation from forming private armies" on Ukrainian soil.

The long-simmering conflict bubbled over Sunday when Russian border guards rammed into and opened fire on three Ukrainian vessels near the Crimean Peninsula, which Moscow annexed in 2014.

The vessels were trying to pass through the Kerch Strait on their way to the Sea of Azov. The Russians then captured the ships and their 24-member crew.

The Ukrainian parliament on Monday also adopted a motion from Poroshenko to impose martial law in the country for 30 days in the wake of the standoff.

A detained Ukrainian sailor — one of 24 currently detained by Russian authorities — is escorted to a car after a court hearing in Simferopol, Crimea, on Wednesday. (STR/AFP/Getty Images)

There has been growing hostility between Ukraine and Russia since Moscow's annexation of the Crimean Peninsula from Ukraine in 2014. Russia has also supported separatists in Ukraine's east with clandestine dispatches of troops and weapons. Fighting there has killed at least 10,000 people since 2014 but eased somewhat after a 2015 truce.

Friday's announcement follows Thursday's decision by U.S. President Donald Trump to scrap his much-anticipated meeting with Russian leader Vladimir Putin. Trump said it wasn't appropriate for him to meet with Putin since Russia hasn't released the Ukrainian seamen.

"We don't like what happened. We're not happy about it. Nobody is. But hopefully they'll be able to settle it out soon because we look forward to meeting with President Putin," Trump said in Buenos Aires on Friday.

"But on the basis of what took place, with respect to the ships and sailors — that was the sole reason."

Donald Tusk, the European Council's president, said Friday the EU is expected to extend sanctions on Russia, calling the Ukrainian ships' seizure "totally unnacceptable."

"Europe is united in its support for Ukraine's sovereignty and territorial integrity," Tusk told reporters on the sidelines of this weekend's G20 summit in Argentina.

Senior cleric under investigation

Meanwhile, Ukraine's intelligence agency announced on Friday that it is investigating a senior cleric of the Russian Orthodox Church.

Ihor Guskov, chief of staff of the SBU intelligence agency, told reporters that its officers are searching the home of Rev. Pavlo, who leads the Pechersk monastery in Kyiv. He said the cleric is suspected of "inciting hatred."

The monastery, which is the spiritual centre of Ukraine, is under the jurisdiction of the Russian Orthodox Church.

The Ukrainian church, which has been part of the Russian Orthodox Church for centuries, has moved closer to forming an independent church — fuelled by conflict with Russia Ukraine's Orthodox communities earlier this year.

There are three Orthodox communities in Ukraine, including two breakaway churches. Ukrainian authorities have sought to portray Russian Orthodox clerics in Ukraine as supporting separatists.

Ukraine's president announced on Thursday that the Constantinople patriarchy has approved a decree granting the Ukrainian Orthodox Church independence from the Russian Orthodox Church, a major boost to the president's approval ratings.

Russian ships fired Sunday on three Ukrainian vessels attempting to pass through a strait that Russia has effectively controlled since it annexed Crimea in 2014. Since then, a freighter ship has blocked the only entrance in and out of the waterway. (CBC)

Both the Russian Orthodox Church and Russian authorities are strongly against the move, and have warned Ukraine not to do it, fearing sectarian violence.

Russia's government-appointed ombudsman for Crimea told Russian news agencies that all the captured seamen have been transported from a detention centre in Crimea.

Russian TV station Dozhd on Friday quoted Kogershyn Sagiyeva, a member of the Moscow oversight council that is allowed to inspect prisons, as saying that 21 seamen have been transferred to the Moscow Lefortovo jail while three other seamen are in a hospital in another jail. She said she met with some of the seamen and they appeared to be in good shape.

A Crimea court earlier this week ruled to keep the Ukrainian seamen behind bars for two months pending the investigation.