British PM Theresa May on Thursday warned EU leaders that Russia posed a threat to the whole bloc.

BRUSSELS (AFP) - British Prime Minister Theresa May on Thursday warned EU leaders that Russia posed a threat to the whole bloc as she sought united backing against Moscow after the poisoning of an ex-spy in England.

May told her colleagues at a Brussels summit the attack on Sergei Skripal and his daughter Yulia in the city of Salisbury using a deadly Soviet-developed nerve agent showed the Russian menace "doesn t respect borders".

Her warning came as a British police officer who was also contaminated in the March 4 attack was released from hospital.

While the US, France and Germany have swung behind London, saying they accept the UK assessment that the Russian state is the only plausible culprit, other EU countries keen to protect their Kremlin ties -- notably Greece and Italy -- want a softer line.

"It is clear that the Russian threat doesn t respect borders and indeed the incident in Salisbury was part of a pattern of Russian aggression against Europe and its near neighbours," May told reporters as she arrived in Brussels.

She is expected to tell them over dinner that the threat from the east will continue "for years to come", and long after Britain leaves the bloc in 2019.

The British leader will hold crisis talks on the poisoning with French President Emmanuel Macron and German Chancellor Angela Merkel before briefing all the EU leaders on the investigation.

She also met the leaders from the Baltic states and Denmark, Sweden and Finland who "strongly supported" London s conclusions, a senior British official said.

The poisoning has triggered a furious diplomatic row between London and Moscow, with tit-for-tat expulsions of diplomats on both sides, while the Kremlin denies any responsibility and Russian state media have offered numerous alternative explanations.

Russian President Vladimir Putin convened a meeting of his national security council on Thursday to discuss "Britain s hostile and provocative policy towards Russia", according to a Kremlin statement.

The war of words took a fresh turn Thursday as the Kremlin slammed as "disgusting" comments by British foreign minister Boris Johnson about President Vladimir Putin seeking to exploit Russia s football World Cup in the way Adolf Hitler had used the 1936 Berlin Olympics.

British officials have been pressing European allies to follow London s lead with their own expulsions of Russian diplomats, and Lithuania s outspoken President Dalia Grybauskaite said she was giving serious thought to the matter.

"All of us we are considering such measures," Grybauskaite said as she arrived for the summit.

A French presidency source said Paris was also ready to act. "Some countries, like France, are ready for possible measures to be decided at a national level in cooperation with other European countries," the source said.

EU leaders will issue a statement on the Salisbury attack on Thursday, with a draft seen by AFP saying they will "coordinate on the consequences" for Russia but stopping short of blaming Moscow or mentioning sanctions.

Some countries are pushing to toughen up the statement to bring it in line with last week s joint declaration by Britain, France, Germany and the US pointing the finger at Russia.

But a dissenting rump including Greece, Italy, Cyprus and Austria, keen to preserve their good relations with Moscow, has pushed for the watered-down version, which says only that the EU takes "extremely seriously" London s view that Moscow was to blame.

Greek Prime Minister Alexis Tsipras urged caution in the response over Salisbury, saying "we have to be very responsible".

Other leaders including Bulgarian Prime Minister Boyko Borisov and Luxembourg Prime Minister Xavier Bettel said they needed to see more evidence.

In Britain, a court gave permission to take blood samples from Skripal and his daughter -- who are in a coma in a critical but stable condition -- for testing by the world chemical weapons body, which is probing the incident.

The poisoning comes with worries running high across Europe about Russian meddling -- from repeated cyber attacks to what the EU has called an "orchestrated strategy" of disinformation aimed at destabilising the bloc.

Aside from Salisbury, the two-day summit will also discuss news from Washington that Europe would be excluded for now from President Donald Trump s new US tariffs on steel and aluminium imports.

The leaders will also discuss the scandal over harvested data from Facebook used by a British consulting firm employed by Trump s 2016 campaign team, linking the issue to election meddling.

May will depart the summit on Thursday evening, leaving the remaining 27 on Friday to approve a post-Brexit transition period and adopt guidelines for talks on future relations including a trade deal.