A new intercontinental ballistic missile so secret it has no name yet has been successfully tested in Russia.
The new weapon is designed to penetrate NATO's European missile defence shield.
The test came days after NATO said its system had reached "interim operational capability".
It was reportedly the second test of the missile, the first in September having failed.
Moscow has accused NATO of seeking to undermine its nuclear deterrent but the alliance says its shield is aimed at potential rogue states like Iran.
A military source said the new ICBM used a "new type of fuel that helps reduce the time required to operate the rocket.
Officials believe this makes it more difficult to detect and easier to manoeuvre.
Interfax said the weapon also features individual warheads that can change course to avoid being shot down.