The Ukrainian parliament has implemented Martial Law in response to the escalating tensions between Ukraine and Russia, following a troubling incident at the Kerch Strait. The Russian Navy is alleged to have seized three Ukrainian vessels as they attempted to pass through the strait on Sunday. This is the first time the two militaries have come into open conflict recently, but Ukraine have been in conflict with Russian-backed separatists since 2014.

Here’s what you need to know about the unfolding tensions between the two countries.