PARIS, March 15 (Xinhua) -- France agreed with Britain that Russia was responsible for the poisoning of a former spy in Britain, President Emmanuel Macron's office said Thursday.

On March 4, former Russian intelligence officer Sergei Skripal and his daughter were found unconscious on a bench in a shopping center in the southern British city of Salisbury. They remain in critical but stable condition.

"Since the beginning of the week, the United Kingdom has kept France closely informed of the evidence gathered by British investigators and evidence of Russia's responsibility in the attack," the Elysee said in a statement.

"France agrees with the United Kingdom that there is no other plausible explanation and reiterates its solidarity with its ally," it added.

During a phone conversation with British Prime Minister Theresa May, Macron mentioned the need to coordinate a European response to the nerve agent attack on the Russian spy on British territory.

On Wednesday, May announced that 23 Russian diplomats would be expelled, the biggest move of its kind in three decades.

May blamed Moscow for the chemical attack which involved "military-grade nerve agent of a type developed by Russia."

Russian denied any involvement in the poisoning incident.

Earlier on Thursday, Russian Foreign Ministry spokeswoman Maria Zakharova said London's accusations were "completely insane," adding that "reciprocal steps" would be taken in the near future in response to London's retaliations, including suspending all planned high-level bilateral contacts.