The United States announced on Monday that President Trump has ordered the expulsion of 60 Russian diplomats, joining a bevy of other European nations taking similar actions following the use of a Soviet-era nerve agent on a former Russian spy on British soil.

Although UK officials have permitted international access to the substance recovered from the site of the attack in Salisbury, England, their own tests have confirmed that the substance used to poison Sergei Skripal, a former Russian intelligence officer turned British informant, and his 33-year-old daughter on March 4th, was indeed Novichok — a nerve agent developed and produced by the Soviet Union in the 1980s.

Novichok was created specifically to circumvent existing treaties forbidding the use of chemical weapons and nerve agents. Designed to use no substances included on the banned chemical weapons lists, Novichok is transported as a binary agent that is incredibly difficult to detect, but once combined, becomes one of the most deadly nerve agents ever concocted.

Despite Moscow’s varied, and often contradictory, claims as to how a specifically Soviet weapon was used in an attempted assassination against a man that betrayed the Russian government, British Prime Minister Theresa May has been steadfast in her condemnation of Russia’s involvement in the matter. Soon after the incident, which saw more than 30 other British citizens hospitalized after being exposed to the nerve agent, Theresa May issued an ultimatum to the Russian government: explain yourselves or there will be consequences.

“Should there be no credible response, we will conclude that this action amounts to an unlawful use of force by the Russian state against the United Kingdom, and I will come back to this House and set out the full range of measures we will take in response,” she said at the time.

With the deadline now long gone, May has already ordered the expulsion of 23 Russian diplomats from British soil, and with more than a dozen nations, including the United States, now joining the Brits in their stand against the newly reelected Russia president, it would seem the effort is quickly picking up steam.

“To the Russian government we say: when you attack our friends, you will face serious consequences,” a senior U.S. administration official told reporters, speaking on condition of anonymity.

The sixty Russian officials being expelled from the United States include 12 intelligence officers assigned to the United Nations headquarters in New York City, as well as the closing of a Russian consulate in Seattle. This is the first such expulsion of Russian officials from the United States since December of 2016, when President Barack Obama ordered the expulsion of 35 Russian diplomats as a result of Moscow’s meddling efforts in the presidential election of that same year. Poland, Italy, Denmark, France and Germany were among the 14 members of the European Union to take similar action against the Russian government.