The waters near the Crimean peninsula were the site of a tense standoff between Russian and Ukrainian ships that involved a chase, some gunfire, and fighter jets, followed by strong statements from Moscow and Kiev.

The Ukrainian vessels were sailing between two Ukrainian ports: from Odessa in the Black Sea to Mariupol in the Azov Sea. The only waterway that connects these is the Kerch Strait between Crimea and mainland Russia. Kiev says it notified Moscow in advance that its navy ships would be sailing through the area. Moscow denies that it was given warning.

While both Russia and Ukraine have freedom of navigation in the Kerch Strait under a 2003 treaty, there are detailed technical rules on how vessels should pass through the narrow, complex waterway. All traffic in the area is controlled by the Crimean sea port of Kerch, and every ship should contact the facility, report her route and destination, and receive permission to sail through the Strait.

At around 7am Moscow time (4am GMT) on Sunday, two artillery boats and a tugboat belonging to the Ukrainian Navy crossed the Russian maritime border in the Black Sea and headed to the Kerch Strait.

These ships had not followed the procedure, said the Russian Federal Security Service responsible for maintaining order at the border.

The Russian officers repeatedly asked the Ukrainian vessels to leave Russia's territorial waters, but they ignored those requests. The ships also entered waters that had been temporarily closed to navigation.

Meanwhile, around 11:30am Moscow time (08:30am GMT), two more Ukrainian vessels departed the Azov Sea port of Berdyansk and approached the Kerch Strait from the other side, but then turned back and returned to port.

A giant bulk freighter accompanied by several Russian military vessels blocked the only passage through the Kerch strait for security reasons. The Russian military also scrambled aircraft, while the situation remained tense. Videos from the site showed Russian Ka-52 gunships cruising under the Crimea Bridge. Later, they were joined by several Su-25 strike fighters.

Ukrainian vessels continued their journey despite warnings from the Russian authorities. The Ukrainian Navy said the military vessels were sailing from the port city of Odessa to the Azov port of Mariupol as part of a scheduled routine transfer and claimed that it warned the Russian authorities about the trip in advance.

The FSB denounced the actions of the Ukrainian vessels as "provocation." A video released by Russian authorities shows the Ukrainian vessels maneuvering in close proximity to the Russian ones.

At midnight, the FSB released a statement, saying that Russian warships had to open fire after the three Ukrainian ships ignored "legal demands to stop" and continued "performing dangerous maneuvers."

Three Ukrainian sailors were wounded and given medical assistance, while the ships were seized. The group of ships that were heading to the strait from the Azov Sea turned back to their port.

VIDEO of Ukrainian vessels in the port of Kerch:

Kiev uses "bandit methods" to achieve its goals, the Russian Foreign Ministry's spokeswoman, Maria Zakharova, said following the incident near the Kerch Strait. Ukraine "first stages a provocation, then plays power games, and [eventually] accuses [another side] of aggression," she continued.

Around midnight, Ukrainian President Petro Poroshenko instructed the National Security and Defense Council of Ukraine (NSDC) to convene for an emergency meeting proposing to impose martial law. The council has moved forward with the motion. The Verkhovna Rada, the Ukrainian parliament, will vote on whether to approve the decision in an extraordinary session on Monday.

Poroshenko stated that martial law will not mean immediate mobilization of troops and said that no offensive operations are being planned.

Russia, in turn, called for an extraordinary meeting of the UN Security Council, also scheduled for Monday. The agenda consists of a single item: “Maintenance of international peace and security.”

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