Germany and France are to impose new sanctions on Russia over the UK gas attack, with some measures due as early as Monday (26 March).

"We, Germany and France, agreed that such reactions in addition to the recall of the [EU] ambassador are necessary," German chancellor Angela Merkel said at a joint press briefing with French president Emmanuel Macron in Brussels on Friday.

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New sanctions were 'obvious', Emmanuel Macron said (Photo: consilium.europa.eu)

She declined to say what the new sanctions might be, but she called the UK incident a "very grave challenge to common security".

Macron said it was "obvious" that France would take further action.

"We consider this attack a serious challenge to our security and European sovereignty so it calls for a coordinated and determined response from the European Union and its member states", he said.

He added that French experts had come to "the same technical conclusions" as British ones on the case in a "very clear way".

They spoke after a summit at which the EU blamed Russia for trying to kill a former spy in the UK using a chemical weapon and recalled the EU ambassador to Russia from Moscow.

New EU-level sanctions on Russia might wait until another summit in June, the Danish leader, Lars Lokke Rasmussen indicated.

There might be more information on EU-level measures in April already, European Council head Donald Tusk added.

But like-minded EU states might start expelling Russian diplomats as early as Monday, in a group that includes the Czech Republic, the Baltic states, Denmark, France, Ireland, Poland, and Sweden.

"We'll now consider in the coming days … whether we want to take individual action relating to Russian diplomats in Ireland", Irish leader Leo Vardakar said.

Lithuania's Dalia Grybauskaite said: "From the beginning of next week, a lot of countries, we will go for our national measures.

Other countries were wary of escalating tension with Russia.

"It is important that this condemnation [of Russia's actions] would not automatically trigger an escalation, or close the necessary space for dialogue with Russia at this geopolitically sensitive moment," Italian prime minister Paolo Gentiloni told press.

He pledged "solidarity" with the UK, adding: "It has always been said that Brexit doesn't mean rupture or change in political and strategic relations" between the UK and the EU.

Tusk said it was difficult to imagine what might be an "adequate" reaction to Russia's unprovoked chemical attack on the UK.

"We cannot respond adequately because we're completely different from the perpetrator of this attack, if you know what I mean," he said.

European Commission president Jean-Claude Juncker noted that the recall of the EU ambassador to Russia was an "unprecedented step".

Meanwhile, Russian officials continued to deride the British and EU accusations on Friday.

"The idea of EU solidarity is above common sense", Russian deputy foreign minister Sergei Ryabkov told state news agency Tass.

"Naturally, the European Union is general and each of its members individually may take any decisions [sanctions] they think right, but, obviously, consequences of such decisions will be double-edged … the consequences of these choices will certainly cut both ways," he added.