The Kremlin has denied US claims that Russia's nuclear-powered cruise missile with “unlimited” range crashed after only 22 miles.
The weapon was one of a range of “invincible” nuclear arms announced by Vladimir Putin during a speech in March.
“Since its range is unlimited, it can manoeuvre as long as you want,” Mr Putin said. “For now, no one in the world has anything like this.”
But sources with direct knowledge of a US intelligence report told CNBC that four tests of the missile between November and February all resulted in crashes.
The longest flight lasted two minutes and covered 22 miles, while shortest ended only four seconds and five miles after launch, they said.
CNN previously quoted a US official as saying the cruise missile had crashed during tests.