It's “overwhelmingly likely” Russian President Vladimir Putin ordered the military-grade nerve agent attack on a former double agent on British soil, the U.K. foreign secretary said Friday.

Boris Johnson, while visiting the Battle of Britain Bunker museum in Uxbridge with his Polish counterpart, told reporters the British government has “nothing against” the Russian people and that their problem is with the Kremlin.

“Our quarrel is with Putin’s Kremlin, and with this decision, and we think it overwhelmingly likely that it was his decision to direct the use of a nerve agent on the streets of the U.K., on the streets of Europe, for the first time since the Second World War,” he said. “That is why we are at odds with Russia.”

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Russia was quick to deny the accusation and reiterated it was not involved in the poisoning of Sergei Skripal, 66, and his 33-year-old daughter, Yulia, in Salisbury nearly two weeks ago using nerve agent Novichok.

Putin spokesman Dmitry Peskov said in a statement Johnson’s claim was a “shocking and inexcusable breach of diplomatic propriety.”

Johnson’s remarks are the first to directly blame Putin for the incident, which has threatened international relations.

U.K. Prime Minister Theresa May said it’s “highly likely” the Kremlin is responsible for the March 4 attack against Skripal and his daughter. The two, along with a police officer who was the first to aid the pair, remain hospitalized.

Britain has expelled 23 Russian diplomats and suspended high-level contacts with Moscow due to the incident. Government officials and members of the Royal Family will also not be attending the soccer World Cup to be held in Russia later this summer.

On Thursday, in a rare joint statement, the leaders of the United States, Germany and France joined May in accusing Russia of being behind the attack.

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"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. It threatens the security of us all,” the statement said.

The quartet wrote “there is no plausible alternative explanation” except Russian responsibility for the attack on British soil, and the Kremlin’s failure to respond to a “legitimate request” for an explanation “further underlines its responsibility.”

“We call on Russia to live up to its responsibilities as a member of the UN Security Council to uphold international peace and security,” the statement said.

Russia is expected to take retaliatory measures soon.

Amid the heightened tension between the two countries, it was announced Friday that Arsenal F.C. will play CSKA Moscow in the quarter-finals of the Europa League.

The Associated Press contributed to this report.