In the statement, the four leaders said they shared the view of British investigators that “there is no plausible alternative explanation” for the attack. They added that “Russia’s failure to address the legitimate request by the U.K. government further underlines its responsibility.”
Prime Minister Theresa May had asked Moscow to explain how Novichok, a military-grade nerve agent developed by Russia, came to be used in the town of Salisbury. She posited that either Russia was directly involved or it had lost control of a chemical weapon. Moscow responded to the ultimatum with scorn and sarcasm, ultimately blowing off May’s demands.
“It is an assault on U.K. sovereignty and any such use by a state party is a clear violation of the Chemical Weapons Convention and a breach of international law,” the four leaders said in their statement, released by May’s office.
“It threatens the security of us all,” they added, without spelling out any possible further reprisals by the United Kingdom and its allies.
Asked by reporters Thursday whether Russia was behind the attack, President Trump said, “It looks like it.”
“I spoke with the prime minister, and we are in deep discussions — a very sad situation,” Trump said. “It certainly looks like the Russians are behind it, something that should never, ever happen.” He added that his administration was taking the attack “very seriously.”
“The answer will come very soon, I assure you,” Foreign Minister Sergei Lavrov said Thursday. “You know that we, as polite people, will first communicate this response to our British colleagues.”
In Britain, May received widespread support for her decision to expel the 23 Russians believed to be involved in espionage and to suspend high-level meetings between British and Russian officials. The left-leaning Guardian wrote in an editorial that May was right to set out a “measured retaliatory response.” The right-leaning Daily Telegraph said the prime minister could have gone further, but nonetheless praised her response as “commendably robust.”
Analysts said that while May did announce concrete measures, she was also holding back in the event that Britain wanted to escalate its response later on.
The British government will want to have “weapons in the armory,” said James Nixey, head of the Russia and Eurasia program at Chatham House, a London-based think tank.
On Thursday afternoon, May made her first appearance in Salisbury since the attack, speaking there with officials and residents.
“We do hold Russia culpable for this brazen, brazen act and despicable act that’s taken place on the streets of what is such a remarkable city,” she told the BBC after viewing the site where the Skripals were found slumped over on a park bench — one of several areas that remain cordoned off as police continue their investigation.
Officials and pundits in Moscow have issued a steady stream of denials and counterclaims, a tactic that continued Thursday.
Kremlin spokesman Dmitry Peskov said that President Vladimir Putin met with members of his national security council Thursday for a “detailed discussion” on the situation with Britain. “Extreme concern was expressed in connection with the destructive and provocative position taken by the British side,” he said.
Lavrov reiterated that the allegations were “boorish and unfounded.” The actions taken by the British “go beyond the limits of elementary rules of decency,” he said, while asserting that Russia has attempted to handle the matter in a civilized manner.
Russia’s deputy foreign minister, Sergei Ryabkov, told the Interfax news agency later Thursday that Russia ceased development of new chemical weapons immediately after joining the Chemical Weapons Convention, which was signed in 1993. He also insisted that neither Russia nor its predecessor, the Soviet Union, developed a nerve agent called Novichok, and he dismissed the accusations as a pretext for the United States to delay the final destruction of its chemical weapons stockpiles.
Russia declared last year that it had finished destroying its chemical weapons stockpiles and chided the United States for lagging behind. A 2012 deadline called for complete destruction of the weapons, but both sides failed to meet it. The United States has said it intends to finish the process by 2023. Novichok was believed to have been developed in the late 1980s, as the Soviet Union was negotiating the convention, to skirt the agreement’s requirements.
Most of Russia’s denials have not gone so far as to deny that Novichok was ever created. Alexei Chepa, deputy head of the State Duma’s Foreign Affairs Committee, suggested that Britain could have received Novichok via the United States as part of a plot to frame Russia — one of several explanations forwarded by Russian officials and commentators.
Russia has also asked Britain for access to the poison and its victims, 66-year-old Skripal and his 33-year-old daughter. Both are reported to remain in comas.
Skripal was jailed in Russia in 2006 for selling state secrets to British intelligence but he was released in 2010 as part of a high-profile spy swap.
When asked how Britain might respond to any retaliation, British Defense Secretary Gavin Williamson said that Russia “should go away; it should shut up.”
He was taking questions after a speech announcing a $67 million investment in a new chemical weapons defense center.
In Brussels, NATO Secretary General Jens Stoltenberg said the defense alliance stands ready to provide support to Britain. Russia is responsible for a “blurring of the line between peace, crisis and war,” Stoltenberg said, calling the Kremlin’s behavior “destabilizing and dangerous.”
So far, Britain has held back from triggering NATO’s one-for-all, all-for-one collective defense clause that would activate a coordinated military response from the 29 member nations. NATO officials have suggested that the nerve-agent attack probably does not rise to that level. But the alliance is engaged, Stoltenberg said.
British national security adviser Mark Sedwill briefed NATO ambassadors on Thursday. “What happened in Salisbury was the latest in a clear pattern of reckless and unlawful behavior by the Russian state and concerns the whole alliance,” he said afterward.
Stoltenberg will meet Monday with British Foreign Secretary Boris Johnson.
Writing in The Washington Post on Thursday, Johnson said that “all responsible nations share an obligation to take a principled stance against this behavior,” which he characterized as part of a larger pattern of “reckless behavior” by Putin. The nerve agent, Novichok, was selected for a reason, he said.
“In its blatant Russian-ness, the nerve agent sends a signal to all who may be thinking of dissent in the intensifying repression of Putin’s Russia,” Johnson wrote. “The message is clear: We will find you, we will catch you, we will kill you — and though we will deny it with lip-curling scorn, the world will know beyond doubt that Russia did it.”
Analysts said Britain is bracing for a tit for tat.
“If you’re not prepared to take a few blows, you shouldn’t make any punches,” Nixey said. “The question is, where does it stop?”
Bodner reported from Moscow. Michael Birnbaum in Brussels, James McAuley in Paris and Philip Rucker and Brian Murphy in Washington contributed to this report.