Trump on Friday announced the movement of the submarines on Truth Social after sparring online with Medvedev, now deputy chairman of Russia's Security Council, and telling Russia Tuesday it had "10 days from today" to agree to a ceasefire in Ukraine or be hit with tariffs.

Medvedev on Monday accused Trump of engaging in a "game of ultimatums" and the American president told him to "watch his words"—a sentiment that was met with a reminder from Medvedev that Russia possesses Soviet-era nuclear strike capabilities of last resort.

Trump on Friday said he’d ordered the movement of the submarines “just in case these foolish and inflammatory statements are more than just that. Words are very important, and can often lead to unintended consequences, I hope this will not be one of those instances.”

This is a developing story and will be updated.