On Sunday, two Ukrainian naval gunboats and a tug departed from the Black Sea port of Odessa, bound to Mariupol in the Sea of Azov. As they approached the Kerch Strait, connecting the Black Sea and the Sea of Azov, they were intercepted by Russian border patrol vessels. One Russian vessel apparently rammed the tug and others later opened fire on the two gunboats. The Russians subsequently seized the three Ukranian vessels. Twenty-four Ukrainians were taken prisoner. Six Ukrainian sailors were reported to be injured. The Russians also blocked the Kerch Strait by anchoring a tanker across the channel. On Monday, the Russians reopened the strait. 

The Russians have accused the Ukrainians of violating their territorials waters whereas the Ukrainians charge that the Russians have violated a bilateral treaty guaranteeing free access to ships of both nations to the Kerch Strait, the Sea of Azov and the Black Sea. Ukrainian lawmakers on Monday voted to introduce martial law in the border areas with Russia.

Ukraine says Russia opened fire on its naval vessels