Russian authorities suspended the passage of commercial vessels in the Azov Sea until further notice, according to a statement by the state agency for maritime and river transport Thursday.
Ukraine and Russia both have ports in the Azov Sea, including Ukraine's major port of Mariupol, while Russia controls the sea's mouth at the Kerch Strait.
Russia's ground forces on Thursday crossed into Ukraine from several directions, Ukraine's Border Guards Service said, hours after President Vladimir Putin announced the launch of a major offensive.
Ukraine's Border Guards said Russian tanks and other heavy equipment crossed the frontier in several northern regions, as well as from the Kremlin-annexed Crimean peninsula in the south.
