MOSCOW (AP) — The Ukrainian parliament is set to consider a presidential request for the introduction of martial law in Ukraine following an incident in which Russian coast guard ships fired on Ukrainian navy vessels.

Ukraine's navy said six Ukrainian seamen were wounded when Russian coast guards opened fire on three Ukrainian ships near the Kerch Strait and then seized them late Sunday.

The two nations traded blame over the incident that further escalated tensions that have soared since Russia annexed Ukraine's Crimean Peninsula in 2014 and backed a separatist insurgency in eastern Ukraine.

Ukraine said its vessels were heading to the Sea of Azov in line with international maritime rules, while Russia charged that they had failed to obtain permission to pass through the narrow Kerch Strait separating Crimea from the Russian mainland.