UK prime minister to tell European Council that use of the Novichok nerve agent was “a clear violation” of international law.

LONDON — Theresa May will warn EU leaders over dinner in Brussels Thursday that Russian spy networks in Europe are a threat to the whole of the bloc that will last for “years to come.”

The U.K. prime minister’s message comes as Britain steps up efforts to persuade its closest allies to follow the U.K.’s lead imposing diplomatic sanctions against Moscow in response to the first use of chemical weapons on European soil since the Second World War.

According to an advance briefing from the U.K. government, May will say the attack on the Russian double agent Segei Skripal in Salisbury earlier this month was “an indiscriminate and reckless act against the United Kingdom” amounting to “attempted murder using an illegal chemical weapon that we know Russia possesses.”

May will go on to say that other countries share the U.K.’s assessment that Russia is “responsible” for the attack before warning that the use of the Novichok nerve agent was “a clear violation” of international law.

The prime minister will warn EU leaders that Russia’s “disrespect for international rules and norms clearly threatens the basis for our advanced democracies, open societies, and free economies.”

She will add: “The Russian threat does not respect borders, and as such we are all at risk.”

The prime minister will warn EU leaders that Russia’s “disrespect for international rules and norms clearly threatens the basis for our advanced democracies, open societies, and free economies.”

A senior Whitehall official told reporters in London the U.K. was “not looking for confrontation or regime change” with Moscow but warned that Russia was now considered a “strategic enemy” by London and not a “strategic partner.”

According to the prime minister’s official spokesman May will tell EU leaders the U.K. has expelled 23 undeclared Russian intelligence officers and the incident in Salisbury “has shown the threat that Russian networks pose to all our national security.”

Despite the wording of the Council conclusions, leaked to POLITICO Wednesday, which does not directly attribute blame for the attack to Moscow, May will insist the U.K. is happy with the support shown by its allies. “We welcome the backing that has been shown by EU leaders so far,” she will say.

“We want to work with our EU allies to uphold and protect the international rules-based order, to hold Russia to account for this flagrant breach of international laws, to ensure that such a heinous crime is never repeated, to protect our shared security in the face of the long-term challenge that Russia poses.”

According to a senior government official, the prime minister will end by warning that the challenge of Russia is one that will endure for “years to come.”