Brussels (AFP) - The poisoning of a former Russian spy in Britain was an "attack on European sovereignty", French President Emmanuel Macron said Friday after EU leaders backed London's assessment that Moscow was to blame.

Diplomatic pressure is building on Moscow over its role in the nerve agent attack on Sergei Skripal and his daughter Yulia in the English city of Salisbury.

The European Union is recalling its ambassador to Moscow for consultation and a number of member states are considering following Britain's lead and expelling Russian intelligence agents posing as diplomats.

Latvia has already said it will make expulsions, EU President Donald Tusk said more steps were expected as early as Monday and German Chancellor Angela Merkel said further coordinated actions were "necessary" to respond to the attack.

"We see this attack as a serious challenge to our security and as an attack on European sovereignty," Macron told a joint news conference with Merkel after a summit in Brussels.

"It calls for a coordinated, determined response from the European Union and its member states."

May briefed other EU leaders on the probe into the Salisbury attack over a summit dinner on Thursday.

She managed to overcome resistance from countries like Greece and Italy who were reluctant to put their close Kremlin ties in jeopardy to persuade them to back Britain's conclusion that Moscow was to blame.

Merlkel said May had shared "certain findings" which left little doubt Moscow was behind the first offensive use of a nerve agent in Europe since World War 2.

"We believe that the analyses are already very well-founded and this has not been questioned by anyone," Merkel said.

"We agreed -- Germany and France at least -- that such reactions are still necessary in addition to recalling the ambassador."

European Commission chief Jean-Claude Juncker said the recall of the ambassador was an "extraordinary measure" never before taken by the bloc.

But divisions remain over how far to go, with Austria already ruling out expelling diplomats.

Tusk said it was not clear how many states would join the expulsions.

"More than one but I don't think that it will be the whole group," he said.