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LONDON—U.K. Prime Minister
said Monday it was highly likely Moscow was behind the poisoning of a former Russian double agent and his daughter, adding the government has summoned the ambassador and demanded an explanation by the end of Tuesday.
Mrs. May told Parliament that Sergei Skripal and his daughter Yulia were poisoned last week with a military-grade nerve agent of the “Novichok” type, originally developed by Russia.
“Either this was a direct act by the Russian state against our country,” Mrs. May said, “or the Russian government lost control of this potentially catastrophically damaging nerve agent and allowed it to get into the hands of others.”
The U.K. has also demanded Russia immediately provide “full and complete disclosure” of the Novichok program to the Organization for the Prohibition of Chemical Weapons, the chemical-weapons watchdog headquartered in The Hague in the Netherlands.
Should Russia offer no “credible” response, Mrs. May said, the U.K. will conclude that the poisoning amounts to an unlawful use of force by the Russian state against Britain.
“And I will come back to this House and set out the full range of measures that we will take in response,” she said.
Russian Foreign Ministry spokeswoman
called Mrs. May’s statements “a circus show in the British Parliament,” Russian news agencies reported.
Mrs. May has faced growing calls for sanctions against the Kremlin, with one prominent ruling-party lawmaker saying the poisoning looked “like state-sponsored attempted murder.” Mr. Skripal and his daughter remain in critical but stable condition.
“It is incumbent upon us to react and, I hope, to lead others to do so,” Tom Tugendhat, a Conservative lawmaker who chairs the parliamentary foreign-affairs committee, told the British Broadcasting Corp. on Monday.
Mrs. May has a wide range of options, from the relatively mundane—expelling diplomats and canceling meetings—to freezing Russian assets or even pushing for a coordinated EU and NATO response.
Successive British governments have been accused by the media and opposition politicians of responding weakly to suspected state Russian activity on British soil, particularly in the 2006 murder of Alexander Litvinenko, a former Russian intelligence agent and Kremlin critic, who suffered a painful death after drinking tea laced with polonium-210.
In 2007 the U.K. expelled four Russian diplomats after Moscow refused to extradite the chief suspects, but after a high-level investigation concluded nearly a decade later that the killing was likely approved by Russian President
the Conservative government imposed no new sanctions.
Any government response to Mr. Skripal’s poisoning will have to be significantly stronger than that, said Anthony Glees, director at the Centre for Security and Intelligence Studies at the University of Buckingham, though it could incur an angry Russian response.
“This time is different,” he said. “The public will not stand for it.”
“The prime minister will need to make it clear to the public that Russia could launch a cyberattack on the U.K. in response,” he said. British officials blamed Russia for June’s massive “Petya” cyberattack, which crippled computer networks at multinational firms. Since Britain has also been investing in cyberdefense capabilities, Mr. Glees said, “We can now dish it out as well.”
The scale of a potential British retaliation depends on how bold and imaginative the government is willing to be, said Mark Galeotti, a senior researcher at the Institute of International Relations in Prague. “The sky is the limit,” he said, adding that the most effective response would be unpredictable. Taking measures Moscow hadn’t foreseen and accepted as a cost of its actions would go beyond punishing Moscow to also serve as a deterrent, he said.
Expulsion of presumed spies from the Russian embassy, curtailing official contacts, including during the coming World Cup in Russia, and calling off bilateral meetings would be “what the usual etiquette requires,” Mr. Galeotti said. “Except the existing tool kit has clearly not worked.”
Britain could instead go after people who are close to the Kremlin, freezing their U.K. assets, or even call off Britain’s participation in the soccer tournament, President Vladimir Putin’s “vanity project,” Mr. Galeotti said.
A multilateral response of the kind imposed by the European Union and U.S. over Russia’s intervention in Ukraine would be most effective, Mr. Galeotti said, because Moscow would be hard-pressed to immediately retaliate in kind.
However, with Britain scheduled to leave the EU next year, and with some EU countries such as Greece taking a less hawkish stance on Russia, such an approach would likely need to rely on “a coalition of the willing,” rather than the EU as a whole, he said.
Britain could also attempt to put the issue on the agenda of the Group of Seven, and bring allies such as the U.S. and Japan on board. The big question, however, would be whether U.S. President
who has so far been reluctant to criticize Mr. Putin, would be willing to sign up. Japanese Prime Minister
has also fostered good relations with the Kremlin.
Russia has largely dismissed the poisoning as a British issue. On Monday Kremlin spokesman Dmitry Peskov said Moscow hadn’t yet heard any official accusations from the U.K. “In any case, it’s not our problem,” he said.
Russia’s relations with the U.K., which has been a hard-liner within the EU on sanctions over Ukraine, are particularly bad at the moment, perhaps worse than with any other Western state, Mr. Galeotti said.
“We could consider that to be liberating,” he said, referring to the potential scope of Britain’s retaliation. “We don’t have that much to lose.”
—Thomas Grove in Moscow, Laurence Norman in Brussels and Jenny Gross in London contributed to this article.
Write to Wiktor Szary at Wiktor.Szary@wsj.com