KYIV, Sept. 23 - Russian naval forces resorted to unsafe military practices against two Ukrainian naval ships and a plane on route to establish a naval base in the Sea of Azov, the Ukrainian navy reported Sunday.

The search and rescue ship A500 Donbas and seagoing tug A830 Korets passed through the Straight of Kerch heading to Berdiansk, where Ukraine wants to set up the base to counter the Russian threat in the region.

But Russian jets and naval ships had ‘committed a number of dangerous incidents,’ including buzzing the ships and the plane and sending their ships in dangerously close proximity with the Ukrainian ships.

“The aggressor country has committed a number of dangerous incidents… grossly violating the requirements of international law and creating an extremely dangerous situation,” the Ukrainian navy reported.

On Friday, the Russian Su-27 jet has come to buzz the Ukrainian military transport plane An-26 over the Black Sea risking a mid-air collision, the navy reported. This comes a day after two Russian naval ships have come in close proximity to the two Ukrainian ships on course to Berdiansk.

During the escalation, Ukraine sent two small armored artillery boats P177 Kremenchuk and P178 Lubny from Berdiansk to help Donbas and Korets, but further escalation had been averted.

Ukraine has been working to establish the naval base in Berdiansk in response to the threat posed by Russian naval ships to commercial maritime traffic over the past six months. Russian ships have been stopping and harassing commercial ships, effectively disrupting trade in the region.

Ukraine decided to relocate two of its naval vessels from the port of Odessa in the Black Sea to Berdiansk in the Sea of Azov as a first step in building up the naval base there.

President Petro Poroshenko on Sunday praised the two Ukrainian ships for passing through the Straight of Kerch into the Sea of Azov despite the threat from the Russian assets.

"Congratulations to the crews of our warships," Poroshenko wrote on his Facebook page. "These ships will be part of the newly created naval base of the Ukrainian fleet in the Sea of Azov."

Kurt Volker, the U.S. special envoy for Ukraine, said earlier this month that Washington would consider providing more lethal arms to Ukraine, in particular to strengthen its forces in the Sea of Azov.

Volker said the U.S. is concerned about the expansion of Russian naval operations in the Sea of Azov, which borders Ukraine, Russia and the Russia-annexed Crimean peninsula.

"We do not accept Russian claims about territory in the waters. We believe the presence of Russian military forces has become a provocative, aggressive step, so we are very concerned about that," he said. (tl/ez)