The North Atlantic Treaty Organisation (Nato) has announced the expulsion of seven Russian employees from Moscow’s observer mission in solidarity with the UK. This is in response to the poisoning of ex-double agent Sergei Skripal and his daughter in Salisbury.

Nato chief Jens Stoltenberg made the announcement on March 27, following the dismissal of more than 140 Russian diplomats from more than 20 different countries. They all believe Russia was behind the attack in Salisbury.

“I have today withdrawn the accreditation of seven staff of the Russian mission to Nato. I will also deny the pending accreditation request for three others,” Stoltenberg told a press conference in Brussels. “This will send a clear message to Russia that there are costs and consequences for their unacceptable pattern of behaviour.”

As reported by Deutsche Welle (DW), Germany’s international broadcaster, Stoltenberg said Russia had exhibited a pattern of disregarding the sovereignty of other nations, going back to the illegal annexation of Ukraine’s region of the Crimea in 2014.

On March 26, the US, Germany, Canada and a number of other countries expelled scores of Moscow diplomats. Russian Foreign Minister Sergey Lavrov described this as “blackmail”.

“We know for certain that this is a result of colossal pressure and colossal blackmail, which is Washington’s chief instrument in the international scene,” said Lavrov. Moscow has promised retaliation for the diplomatic expulsions.

The UK was the first western country to expel Russian diplomats last week over the poisoning in Salisbury in the west of England. Many of the countries to follow suit said they did so out of solidarity with the British government.

Ex-spy Sergei Skripal was freed from Russian custody in 2010 in a “spy swap” with the US. On March 4, he was found nearly comatose on a bench, as was his daughter Yulia. More than 130 people are suspected of having been exposed to the nerve agent used in the attack, a military-grade chemical weapon known as Novichok, which was developed in the Soviet Union in the 1970s.

In a separate report, FRANCE24 noted that the Skripals remain in a critical state in hospital, and Prime Minister Theresa May said “they may never fully recover”.

Meanwhile, British Foreign Secretary Boris Johnson said the mass expulsions were “a blow from which Russian intelligence will need many years to recover”.

The Russian embassy in Washington responded by asking its Twitter followers to vote on which US consulate should be closed, listing those in Vladivostok, St Petersburg and Yekaterinburg as options.