The Nato secretary general, Jens Stoltenberg, said the permanent size of the Russian mission would be cut from 30 to 20 people, adding the announcement was “a clear and very strong message that that there was a cost to Russia’s reckless actions” in poisoning the Russian double agent Sergei Skripal in Salisbury earlier this month.

He claimed Russia had underestimated Nato’s resolve and said the announcements would reduce Russia’s capability to do intelligence work across Nato.

The move came after more than 20 western allies ordered the expulsion of dozens of Russian diplomats in response to the nerve agent attack in the UK, in a show of solidarity that represents the biggest concerted blow to Russian intelligence networks in the west since the cold war.

Speaking in Brussels at the end of consultations with Nato allies on Tuesday, Stoltenberg added that he did not think Russia had expected the west to show such resolve, pointing to the increased Nato military presence on the Russia border, higher defence spending and continued sanctions for Russia’s illegal annexation of Crimea.