Since Mr. Trump launched his war against Iran with Israel in late February, Russia has backed the Iranians with intelligence, including on U.S. assets in the Persian Gulf, and shipped drone components to Tehran via the Caspian Sea. The United States and Iran resumed trading strikes this week after what had been a weekslong hiatus in fighting.

The Financial Times reports Russia is assisting Iran develop ramjet engines for hypersonic cruise missiles under a covert programme.