A Russian coast guard ship emits a green beam to light Ukrainian marine guard boats up after dark.

A coast guard ship of the Russian Federal Security Service (FSB) has staged acts of provocation in the Sea of Azov.

"Tactical groups of boats of the Joint Forces' Mariupol marine guard squad have observed an unusual event in the Mariupol area of the Sea of Azov at about the same time periods, after 21:00 Kyiv time, in the past two days. After dark, marine guard boats of Ukraine's State Border Guard Service were illuminated with a green beam emitted from the direction where one of the ships of the Russia's FSB coast guard has been spotted at a certain distance," the press center of Ukraine's Joint Forces Operation (JFO) Headquarters wrote on Facebook.

Read alsoCrew of Russia's NEYMA tanker detained by Ukraine's SBU freed – Russia's embassy

The JFO HQ says such "lighting effects" lasted for several minutes, no harm to the health of crews or failure of technical equipment after exposure to the beam of green light was recorded.

"However, taking into account that such events took place along the contact line on the ground, appropriate measures have been taken to protect the life and health of personnel," it said.

Territorial units of the military prosecutor's office, the National Police and the SBU Security Service of Ukraine have been informed about such irregularities.

As UNIAN reported, the SBU jointly with the Military Prosecutor's Office on July 25 detained the Russian tanker NEYMA, which blocked Ukrainian naval vessels in the Kerch Strait late in November 2018.

As Ukrainian border guards reported, the NIKA SPIRIT tanker flying the Russian flag entered the port of Izmail on July 24. The international information system EQUASIS identified the vessel as the NEYMA tanker by its IMO number 8895528. This was the tanker used by Russians to block the Kerch Strait last November.

The investigation found the tanker had been renamed NIKA SPIRIT to conceal the involvement of the vessel in illegal actions and an act of aggression, which unfolded on November 25, 2018, when three Ukrainian ships and 24 Ukrainian sailors were detained by the Russian side.

After interrogation, crew members of the Russian tanker NEYMA, returned to Russia.