By Mark Trevelyan
(Reuters) - Russia warned the United States on Wednesday to halt what it called a "spiral of escalation" over Ukraine, but said it would keep informing Washington about test missile launches in order to avoid "dangerous mistakes".
The comments from Deputy Foreign Minister Sergei Ryabkov sent a signal that Moscow, which last week approved a new policy that lowered its threshold for the use of nuclear weapons, wants to keep communication channels open at a time of acute tensions with the U.S.
Ryabkov was speaking six days after Russia launched what it described as a new intermediate-range hypersonic ballistic missile called the Oreshnik against Ukraine - something he said had sent a clear message to the West.
"The signal is very clear and obvious - stop, you should not do this any more, you mustn't supply Kyiv with everything they want, don't encourage them towards new military adventures, they are too dangerous," state media quoted Ryabkov as saying.
"The current (U.S.) administration must stop this spiral of escalation," Ryabkov added. "They simply must, otherwise the situation will become too dangerous for everyone, including the United States itself."
President Vladimir Putin said last week that Russia fired the Oreshnik in response to Ukraine's first use of U.S. ATACMS ballistic missiles and British Storm Shadow cruise missiles to strike at Russian territory with permission from the West.
Ukrainian President Volodymyr Zelenskiy said Russia's use of the new missile - which Kyiv said reached a speed of 13,600 kph (8,450 miles per hour) - amounted to "a clear and severe escalation" in the war and called for strong worldwide condemnation.
The U.S. military said the missile was experimental and that Russia likely possessed only a handful of them.
'VERY DANGEROUS SITUATION'
The Kremlin has said Russia was not technically obliged to warn the United States about the launch of the Oreshnik because it was intermediate-range rather than intercontinental, but that Moscow informed the U.S. 30 minutes before the launch anyway.
"I am sure you understand that this was a stabilising factor in the very dangerous situation in which we currently find ourselves. We are committed to this practice and we hope that the United States will also be committed to it," Ryabkov was quoted as saying.
"And we also hope that such actions will help reduce the risks of miscalculation or dangerous mistakes."
In a separate development on Wednesday, Russia state news agency TASS quoted an official as saying Moscow was continuing work to put its Sarmat intercontinental ballistic missile - part of its strategic nuclear arsenal - on combat duty.
Sarmat is designed to deliver nuclear warheads to strike targets thousands of miles away in the United States or Europe, but its development has been dogged by delays and testing setbacks.
In September, arms experts said Russia appeared to have suffered a catastrophic failure in the missile's latest test, leaving a deep crater at the launch silo.