Russia has said new sanctions imposed by the US over the Salisbury poisoning are “categorically unacceptable”.
Kremlin spokesman Dmitry Peskov also called the sanctions “absolutely illegal”, saying they “do not correspond to international law”.
The US State department said the new sanctions would go into effect this month.
It accused President Vladimir Putin’s government of having used “chemical or biological weapons in violation of international law” in the novichok poisoning of former Russian spy Sergei Skripal and his daughter Yulia.
The announcement sent the rouble plunging to its lowest level against the US dollar since November 2016.
The Russian embassy in the US said it was planning retaliation against what it called “draconian” measures. It said it was considering restricting export of R8-180 rocket engines in response.
:: How Sergei and Yulia Skripal survived the novichok attack
An embassy spokesperson said they “grew accustomed to not hearing any facts or evidence” and reiterated Russia’s position that it has nothing to do with the poisoning.
Russia’s diplomats to the international chemical weapons watchdog said the West was acting as “prosecutor, judge and executioner at the same time”.
The new US sanctions will come into force on 22 August, complying with a 15-day congressional notification period.
Britain has welcomed the news and used it to further attack Russia.
A Downing Street spokesperson said: “The strong international response to the use of a chemical weapon on the streets of Salisbury sends an unequivocal message to Russia that its provocative, reckless behaviour will not go unchallenged.”
Mr Skripal and his daughter Yulia were in intensive care for several weeks after being poisoned with the chemical substance at his home in Salisbury in March.
They were found in a serious condition on a bench in The Maltings shopping centre, and the discovery of the substance sparked a city-wide investigation with police having to cordon off large areas, including where they had eaten dinner that evening.
Three months later, Dawn Sturgess and her partner Charlie Rowley fell ill after they came into contact with the substance, which was found in a sealed perfume bottle. Ms Sturgess later died.
:: Novichok poisonings: Six unanswered questions
The US treasury has already imposed sanctions on Russia for alleged meddling in the 2016 presidential election, taking steps against 19 people and five entities.
Republican strategist Matt Mackowiak told Sky News: “The state department announced they would undertake their own process to come to their own conclusions when this happened.
“This backs up what other intelligence services and the British services have found. It shows the special relationship between the UK and the US.
“President Trump believes there is a way to work with Russia where they have common issues, but their behaviour gets worse, and the US has to be part of the international response.
“Most of the allied nations are relieved to see this step happening today.”
Mr Mackowiak said the sanctions were “significant”, even if their response had been slower than others.
He also said there could be a push from Congress for even greater sanctions amid the investigation into Russia’s alleged meddling in the 2016 election.
It comes after Senator Rand Paul delivered a letter from Mr Trump to Russian president Vladimir Putin which proposed “further engagement in various areas including countering terrorism, enhancing legislative dialogue and resuming cultural exchanges”.
Mr Trump has invited Mr Putin to the White House.
Reports earlier this week that the UK was preparing to request the extradition of two Russians it suspected of being behind the attack were found to be less advanced than initially suggested, Sky sources said.
Russia’s embassy in London said they had not received any extradition requests over allegations any of its citizens were involved in the novichok poisonings.
From – SkyNews