Russia said Wednesday that the world's "top priority" should be to avoid a clash of nuclear powers, stressing it could lead to "catastrophic consequences.""We are firmly convinced that in the current difficult and turbulent situation a consequence of irresponsible and shameless actions aimed at undermining our national security the top priority is to prevent any military clash of nuclear powers," said the Foreign Ministry.Moscow called on other nuclear powers to "abandon dangerous attempts to infringe on each other's vital interests."The Foreign Ministry's statement came amid rising fears of nuclear use in the Ukraine conflict, which has dragged on into its ninth month."Russia is strictly and consistently guided by the tenet that a nuclear war cannot be won and must never be fought," the statement read.It said Moscow's nuclear doctrine is "purely defensive in nature," only allowing the Kremlin to use such weapons in the event of nuclear aggression or "when the very existence of our state is threatened."Russia has repeatedly suggested that Ukrainian territories it claims to have annexed are protected by its nuclear doctrine.The statement called on the world's other nuclear powers the United States, Britain, France and China to "work together to solve this priority task."