Russia says submarine off France surfaced intentionally, denies breakdown reports

"NATO stands ready to defend our Alliance with constant vigilance and maritime awareness across the Atlantic," it posted on social media, without naming the submarine.

VChK-OGPU, a shadowy social media channel that publishes purported Russian security leaks, reported last month that the diesel-powered submarine Novorossiysk was suffering serious technical problems, with fuel leaking into the hold.