Britain yesterday said its ambassador will snub a Moscow meeting on the poisoning of a spy in England as Russia's foreign minister threatened further retaliation against "anti-Russian measures."

The Kremlin slammed the planned absence of British ambassador Laurie Bristow from a meeting being hosted by the foreign ministry, saying it showed London's unwillingness to cooperate.

On Tuesday, Moscow had invited all ambassadors to Russia to a meeting with foreign ministry experts to hear its views on the poisoning of former double agent Sergei Skripal in an English city earlier this month.

Vladimir Yermakov, director of the ministry's non-proliferation and arms control department, will brief foreign embassy representatives at 1200 GMT, an official told AFP.

But several Western diplomatic missions said their chiefs would not go.

The head of European Commission delegation to Russia will also not attend because "he is not the country," its spokeswoman Luca Eszter Kadar told AFP.

The German and French embassies said they planned to send representatives to the meeting.

Russia is facing huge pressure from Britain and its allies to explain how Skripal and his daughter Yulia were poisoned on British soil with a nerve agent the UK says is Soviet-designed.

Moscow has denied being involved. The March 4 attack in the English city of Salisbury has plunged Russia's ties with Britain and its allies into a new crisis.

Britain has thrown out 23 Russian diplomats over the attack, prompting a tit-for-tat response from Moscow.