Russia has angrily denounced the imposition of “draconian” new US sanctions after the administration concluded Moscow was responsible for the Salisbury nerve agent attack.
The embassy in Washington accused the Americans of running a “sanctions assembly line” following the surprise announcement by the State Department on Wednesday.
The Kremlin said the US action was “absolutely unlawful” but played down the prospect of immediate tit-for-tat measures.
The move came despite controversial efforts by Donald Trump to reach out to his Russian counterpart, Vladimir Putin, at last month’s summit in Helsinki.
Unusually, there was no immediate comment by the US president, who has been heavily critical of the investigation into Russian interference in the 2016 presidential election.
Under US legislation, the administration is obliged to act once there has been a determination that chemical or biological weapons have been used.
State Department officials said the sanctions – which are due to come into force around August 22 – were expected to include an export ban on sensitive national security technology and goods.
They could be followed by a second more punitive round of measures if the administration is unable to certify that Russia is no longer using chemical weapons or provide “reliable assurances” that it will not do so in future.
According to US reports, they could include downgrading diplomatic relations, suspending flights to the US by state airline Aeroflot and cutting off many exports and imports.
“We grew accustomed to not hearing any facts or evidence. The American side refused to answer our follow-up questions, claiming that the information is classified. However, we were told that the US has enough intel to conclude that Russia is to blame,” it said.
It added: “We confirmed that we continue to strongly stand for an open and transparent investigation of the crime committed in Salisbury and for bringing the culprits to justice. We suggested publishing our correspondence on this issue. No answer has followed so far.”
In Moscow, Mr Putin’s spokesman, Dmitry Peskov, said they were still waiting for official notification from the US authorities.
“We heard the official statements about the so-called new sanctions and we heard some high-profile source saying that some restrictions could be introduced against Russia,” he told reporters, according to the Tass news agency.
“As we still do not understand what it means officially, it would be definitely wrong to speak of any retaliatory measures now.”
And Ministry for Foreign Affairs spokeswoman Maria Zakharova said the Government’s defence laboratory at Porton Down should be “the focus of investigations”.
“We insist that the British authorities disclose data on the lab’s work to synthesise chemical warfare agents, including the gas labelled Novichok in the West,” she said.
In contrast, the US move was warmly welcomed by Downing Street, which has consistently blamed Moscow for the attack in March on former Russian spy Sergei Skripal and his daughter Yulia with a military-grade Novichok nerve agent developed by the former Soviet Union.
Two other people, Dawn Sturgess and her partner, Charlie Rowley, were subsequently exposed to the nerve agent, believed to have been in a perfume bottle discarded by the attackers. Ms Sturgess died eight days later.
“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.”
And Foreign Secretary Jeremy Hunt said: “If we are going to stop chemical and biological weapons – including nerve agents – becoming a new and horrific 21st century norm, states like Russia that use or condone their use need to know there is a price to pay.
“Thank you USA for standing firm with us on this.”
The US announcement follows reports that the British Government is preparing to submit an extradition request for two Russian nationals wanted in connection with the attack.
They were said to have been identified by cross-checking CCTV footage with records of people who entered the country around the time of the attack. There has been no official comment on the reports.