Washington: US President Donald Trump on Monday ordered the expulsion of 60 Russians from the United States and closed the Russian consulate in Seattle in response to a nerve agent attack earlier this month in Britain, senior U.S. officials said.

It was the toughest action that Trump has taken against Russia, and followed what one of the official called a ‘reckless attempt’ by the Russian government on March 4 to attack former Russian spy Sergei Skripal and his daughter Yulia with a military-grade nerve agent.

The pair were found slumped on a bench in the southern English city of Salisbury and remain critically ill in hospital.

‘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.

Moscow has denied responsibility for the attack and has retaliated against Britain’s expulsion of 23 Russians by ordering out the same number of Britons.

The Kremlin said ahead of the U.S. announcement that it would respond in kind.

The attack was the first known offensive use of a nerve toxin in Europe since World War Two, and European Union member states agreed on Friday to take additional measures against Russia. Germany, France, the Netherlands, Denmark, Poland, Latvia, Lithuania and Estonia announced expulsions of Russians on Monday.

The Seattle consulate in the West Coast state of Washington was selected for closure due to its proximity to a U.S. submarine base and to planemaker Boeing Co, the U.S. officials said.

Trump’s order also included 12 Russians described by the U.S. officials as Russian intelligence officers from Russia’s mission to the United Nations headquarters in New York and reflects U.S. concerns that Russian intelligence activities have been increasingly aggressive.

The U.S. officials said Russian diplomats have been abusing their diplomatic privileges in the United States and around the world.

‘They hide behind the veneer of diplomatic immunity while actively engaging in intelligence operations that undermine the country in which they are hosted in a democracy they seek to minimize,’ an official said.

‘With today’s action, we are removing a large number of the unacceptably numerous Russian intelligence officers who abide in the United States,’ the official said.