Russia has opened fire on Ukrainian ships and captured three vessels in a major escalation of tensions off the coast of Crimea.<br />Three sailors have been wounded after the Ukrainian navy said two gunboats were hit by the strikes in the Black Sea.<br />Both countries have blamed each other for the incident.<br />The crisis began when Russia accused the Ukrainian ships of illegally entering its waters.<br />Russia placed a tanker under a bridge in the Kerch Strait to block the Ukrainian vessels from entering the Sea of Azov.<br />Ukraine said it had informed the Russians of its plan to move its ships through.<br />Ukrainian president Petro Poroshenko has called an emergency session of his war cabinet amid reports that martial law could be imposed.<br />The EU and NATO have called for restraint and urged Moscow to restore freedom of passage at the Kerch Strait. <br />
