The Russian leader was holding his marathon year-end news conference Friday, as the Kremlin sticks to its hardline demands despite U.S. pressure for a peace deal by Christmas.
The vessel is part of Russia's so-called "shadow fleet" - unregulated ships that Kyiv says are exporting large quantities of oil despite Western sanctions.
Kyiv has now expressed readiness to drop its bid to join the NATO military alliance if the U.S. and other Western nations give it similar security guarantees.