British Prime Minister Theresa May will call for European allies to “stand shoulder to shoulder” against the Russian threat that will continue for “years to come.”

“As a European democracy the United Kingdom will stand shoulder to shoulder with the EU and with NATO to face these shared threats together,” May will tell European Union members in an address later Thursday in Brussels, adding that “united we will succeed.”

Moscow’s military-grade nerve agent attack on former Russian spy Sergei Skripal and his daughter, Yulia, earlier this month in Salisbury was “an indiscriminate and reckless act against the United Kingdom” amounting to “attempted murder using an illegal chemical weapon that we know Russia possesses,” she will say, according to released portions of her prepared speech.

Russia’s use of the Soviet-era Novichok nerve agent was a “clear violation” of international law and constitutes a threat against all European nations that requires a unified response, she will say.

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

A senior government official said Britain was “not looking for confrontation or regime change,” but Russia “has shown itself to be a strategic enemy, not a strategic partner.”

May, who last week ordered the expulsion of 23 Russian diplomats she considered spies, wants Britain’s allies to stand up to the Kremlin’s threats.

“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,” May will say.

The United States joined France and Germany last week to sign a statement of solidarity with Britain over the March 4 attack on the Skripals.

But President Trump was roundly criticized for calling Russian leader Vladimir Putin to congratulate him for his election victory — without bringing up Moscow’s meddling in the 2016 election or the nerve agent attack.

The White House defended the call, saying Trump wanted to discuss “shared interests” with the Russian president.

And Trump took to Twitter on Wednesday to make the case that he needs to get along with Putin because Russia can “help solve problems with North Korea, Syria, Ukraine, ISIS, Iran and even the coming Arms Race.”

Moscow has called the accusations “nonsense” and some Russian officials suggested Britain or the United States could have been behind the attack.

With Post wire services