France backs Britain over poison attack

John Irish and Marine Pennetier
AAP

France has agreed with Britain that Russia was behind a nerve agent attack on an ex-spy in England, President Emmanuel Macron's office says as well as urging a united European and trans-Atlantic response.

"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," Macron's office said in a statement issued after a phone call between Macron and Prime Minister Theresa May.

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

"The president and prime minister agreed on the importance of a united European and trans-Atlantic response to this event," Macron's office said.

In contrast to German Chancellor Angela Merkel and US President Donald Trump, who assured May they were taking her government's views seriously, Macron and other French officials were initially cautious about fingering Russia directly.

French government spokesman Benjamin Griveaux said on Wednesday it was too early for Paris to decide whether action should be taken and that a decision would be made only once a case of Russian involvement was proven.

British media were quick to seize on those comments. The Times newspaper ran a front page on Thursday accusing Macron of defying May over the attack.

Paris's nuanced reaction has been in line with Macron's efforts since coming to office in May last year to build a new relationship with Russian President Vladimir Putin.

Rather than directly confronting Putin through threats and "megaphone" diplomacy, he has emphasised private dialogue, while pushing for a restoration of business and cultural ties despite existing European Union sanctions on Moscow.

Late on Wednesday, Foreign Minister Jean-Yves Le Drain sought to address the mixed messages, saying France would be in touch with Britain to coordinate a response.

May announced on Wednesday that Britain was expelling 23 Russian diplomats, and Foreign Secretary Boris Johnson said on Thursday that Britain would target Russian wealth held in Britain. What France could do is unclear.

Officials have declined to say whether he intends to keep that commitment.