Iran has been secretly helping arrange talks between Russia and Yemen's Houthi rebels to send powerful anti-ship missiles to the militant group, according to several Western and regional sources. This deal, which hasn't been revealed until now, shows how close Iran and Russia have become.

The missiles in question, known as Yakhont missiles (also called P-800 Oniks), are highly advanced and capable of hitting ships with incredible accuracy. If the Houthis get their hands on them, it would...