President Donald Trump said he's ordered two nuclear submarines to move in the "appropriate regions" in response to recent comments from Russia's Dmitry Medvedev.

In a social media post, the president described the move as a deterrent prompted by threats by a former Russian leader. It is unclear if any submarines did actually change position.

Russia and China have staged mock combat drills in the Sea of Japan on Sunday in a show of strengthening ties between the countries. Although the war games were planned in advance, they come just one day after Donald Trump moved two US nuclear submarines closer to Russia following comments from former Russian president,