EU Joins U.K. in Denouncing Russia Over Poisoning of Spy

BRUSSELS — Britain’s prime minister, Theresa May, won support from the European Union on Friday over her escalating diplomatic battle with Russia, a significant victory for a leader who has often found herself isolated in Brussels as her country prepares to quit the bloc.

After hours of discussion, European leaders issued a relatively tough statement effectively blaming Moscow for the nerve agent attack on a former Russian spy, Sergei V. Skripal, and his daughter, Yulia, on British soil.

In its declaration of “unqualified solidarity” issued early Friday, the EU said it “agrees” with Britain’s assessment that “it is highly likely that the Russian Federation is responsible and that there is no plausible alternative explanation.”

Although the show of unity is largely symbolic, the EU is expected to withdraw its ambassador to Russia for consultations, and some member nations, including Lithuania, say they are considering expelling Russian diplomats, as Britain did in response to the attack.

The response followed long talks in which May described the reasoning behind Britain’s conclusions that Russia was behind the attack in the quiet cathedral city of Salisbury, including its identification of the chemical used — a strain of the nerve agent Novichok — and its belief that Russia has produced this substance in the last decade.

Welcoming the statement, May said it was right that European nations were “standing together” because the hostile challenge Russia poses “respects no borders, and it is a threat to our values.”

In response, Dmitry Peskov, spokesman for the Russian president, Vladimir Putin, said that he “did not know what the heads of the EU states agreed with” when they offered their support to Britain, as Russia was not given any information.

“We don’t agree with this and repeat that Russia had absolutely nothing to do with the Skripal case,” he said.

Sergei Zheleznyak, a lawmaker from the United Russia party, said that the European Union, under pressure from London and Washington, “was forced to concoct a statement that is vague in content and politicized in essence.”

The declaration was a somewhat surprising success for May, who has often found herself at odds with her European counterparts as she negotiates Britain’s exit from the bloc, a process known as Brexit. The text was tougher than one agreed to earlier this week by EU foreign ministers after talks attended by Britain’s foreign secretary, Boris Johnson.

The issue of relations with Russia divides EU nations sharply, and there is pressure from some to lift economic sanctions against Moscow, so Britain has not pressed for additional steps of that kind. Before the summit meeting, Putin spoke by phone with three EU leaders, the Kremlin announced.

Several countries, including Cyprus and Greece, have close ties to the Kremlin and have been reluctant to take a tougher line. But in traditional EU style, they agreed to the latest text after extracting concessions on other issues — in this case, wording critical of Turkey’s actions in the Eastern Mediterranean and the Aegean, the site of tensions over drilling for gas.

Though the European Union’s show of support for Britain is largely symbolic, it suggests that even after leaving the bloc, London could retain close ties to the bloc on foreign policy, security and defense issues.

On the broader Brexit agenda, things will undoubtedly get difficult again soon. EU leaders were expected to agree Friday to the terms of a 21-month transition deal to prevent a “cliff edge” change in trading rules when Britain officially leaves the bloc next March.

The bloc’s leaders were also expected to pave the way for far-reaching talks on a future trade partnership. Although they will amount to an important time in the Brexit discussions, they will also result in tough negotiations.

EU leaders were also expected to discuss President Donald Trump’s tariffs on steel imports, which went into force Friday. The White House has given some allies, including the European Union, a temporary exemption, giving it until May 1 to negotiate “satisfactory alternative means” to address what it calls a threat to United States national security resulting from current levels of steel and aluminum imports.