Russia received a bitter blow on Thursday when Ukraine’s military announced that it had sunk the pride and joy of its Black Sea Fleet, the Moskva. Unfortunately, that victory may have come at a dangerous cost as experts worry that the Moskva could have been carrying nuclear missiles.

On Friday, Ukrainian experts began speculating that the missile cruiser, the flagship of Russia’s navy in the Black Sea, could have been carrying nuclear-tipped missiles while menacing the coastline near the city of Odesa. Bearing this possibility in mind, several called for an international investigation into the possibility that Moskva went down with warheads onboard.

Andrii Klymenko, an expert at Ukraine's Institute of Black Sea Strategic Studies, wrote on Facebook that there were two nuclear warheads onboard the Moskva at the time of its sinking. Klymenko did not directly cite the source of his information beyond “friends” and “experts”, but the possibility was raised less affirmatively by other Ukrainian analysts.

Mykhailo Samus, deputy director of the Lviv-based Center for Army, Conversion and Disarmament Studies, said on his Facebook page that it was possible the Moskva was carrying nuclear weapons. He suggested the warheads were stored away from conventional munitions when the ship sank, but could remain intact.

The Moskva is a storied warship that first entered service with the Soviet Navy as the Slava in 1979. During the Cold War, the vessel was known to carry nuclear weapons on board and the Russian military has stationed weapon systems capable of firing either conventional or nuclear missiles on the annexed Crimean Peninsula.

But the reality remains foggy on whether or not the Moskva would be carrying nuclear weapons while on patrol of the Ukrainian post.

For its part, the Department of Defense cast doubt on claims that the vessel sank with nuclear arms on board, according to two senior officials who spoke to CNN. The Pentagon confirmed their belief a Ukrainian missile sank the Moskva however, contradicting claims from Russia that it sank during a storm at sea.

These concerns a day after the CIA warned the risk of Russia using a tactical nuke to make up for its battlefield failures should not be taken lightly. Later that evening, the Russian Embassy in Washington D.C. delivered a letter to the State Department warning of “unpredictable consequences” if the U.S. does not cease weapons deliveries to Ukraine.

Russia has insisted it would only use nukes as self-defense against an existential threat, but it has hinted that they remain an option. After ordering his forces into Ukraine, Russia’s President Vladimir Putin warned the West against interfering lest they invite “consequences…never seen in history” and ordered his nuclear forces to enter full alert.