Ukraine attacked the oil export infrastructure that helps fund Moscow’s invasion for the first time on Friday, using a drone strike to damage a Russian naval vessel outside the port of Novorossiysk.

Ukraine’s security services, in collaboration with the country’s navy, carried out the sea drone strikes outside the port, according to two Ukrainian sources with knowledge of the operation. Novorossiysk is a major navy base and oil-exporting port located east of Crimea, which Russia annexed in 2014.

Videos posted on social media, which could not be verified, showed a naval vessel tilted to its side being towed by tug boats back to port. Separate videos released by Ukraine’s armed forces showed footage from a camera mounted on a sea drone as it approached a vessel at night.