Britain, the US, Germany and France have jointly called on Russia to explain a military-grade nerve toxin attack on a former Russian double agent in England which they say threatens Western security.
After the first known offensive use of such a nerve agent on European soil since World War II, Britain has pinned the blame on Russia and has given 23 Russians it said were spies working under diplomatic cover at the embassy in London a week to leave.
Russia has denied any involvement in the poisoning. Foreign Minister Sergei Lavrov accused London of behaving in a "boorish" way and suggested this was partly due to the problems Britain faces over its planned exit from the European Union next year.
- Police investigating after Russian spy allegedly poisoned in New Zealand
- Opinion: Is Russia really behind the attempted murder of double agent Sergei Skripal?
Russia has refused Britain's demands to explain how Novichok, a nerve agent first developed by the Soviet military, was used to strike down Sergei Skripal and his daughter Yulia in the southern English city of Salisbury.
"We call on Russia to address all questions related to the attack," US President Donald Trump, German Chancellor Angela Merkel, French President Emmanuel Macron and British Prime Minister Theresa May said in their joint statement on Thursday.
"It is an assault on UK sovereignty," the leaders said. "It threatens the security of us all."
The statement signals a more co-ordinated response from Britain's closest allies, but it lacked any details about specific measures the West would take if Russia failed to comply.
The Western leaders said the use of the Novichok toxin was a clear breach of the Chemical Weapons Convention and international law.
They called on Russia to provide a complete disclosure of the Novichok program to the Organisation for the Prohibition of Chemical Weapons in The Hague.
Russia says it knows nothing about the poisoning and has repeatedly asked Britain to supply a sample of the nerve agent that was used against Mr Skripal.
Mr Skripal and his daughter have been critically ill since they were found unconscious on a bench in Salisbury, an elegant cathedral city, on March 4. A British policeman who was also poisoned is in a serious but stable condition.
Ms May has directly accused President Vladimir Putin of being behind the attack.
Russia is expected to respond soon to Britain's decision to expel 23 Russian diplomats. Mr Putin discussed relations with Britain at a meeting of Russia's Security Council, Kremlin spokesman Dmitry Peskov said on Thursday.
Ms May on Thursday visited Salisbury, a normally sedate city where police investigators in chemical protection suits and the army have been removing evidence of the poisoning.
NATO Secretary-General Jens Stoltenberg said the attack in Britain was part of a pattern of reckless behaviour from Russia over many years. He said Britain could count on NATO's solidarity, but said there had been no request by London to activate the alliance's mutual defence clause.
Russia will soon expel British diplomats in retaliation for Britain's decision to kick out 23 Russian envoys, Foreign Minister Sergei Lavrov says.
In London on Thursday, Foreign Secretary Boris Johnson ratcheted up the rhetoric against Russia, accusing it of glorying in the attack on Mr Skripal, which he described as a way of scaring anyone who stood up to Mr Putin.
Britain says Russia is responsible for the poisoning with a Soviet-era 'Novichok' nerve agent of Mr Skripal, 66, and his daughter Yulia, 33.
- 'Highly likely' Russia is behind ex-spy poisoning - Theresa May
- 'No evidence' Russia shot down plane, meddled in US election - Peters
Mr Lavrov was quoted by the official news agency RIA as saying the accusations were unacceptable and that British diplomats would be expelled.
But in a series of British media interviews early on Thursday, Mr Johnson said the evidence of Russian guilt was "overwhelming" because only Moscow had access to the poison used and a motive for harming Mr Skripal.
"There is something in the kind of smug, sarcastic response that we're heard from the Russians that to me betokens their fundamental guilt," he told the BBC. "They want to simultaneously deny it and yet at the same time to glory in it."
Mr Johnson said the attack was a way for Putin to send a message to anyone considering taking a stand against it that 'You do that, you are going to die'.
A former agent of the GRU, Russia's military intelligence agency, Mr Skripal betrayed dozens of Russian agents to Britain before being arrested in Moscow and jailed in 2006. He was freed as part of a spy swap deal in 2010 and took refuge in Britain.
Mr Johnson defended the measures announced on Wednesday and suggested that there could be further consequences for wealthy Russians with assets in Britain.
"We will go after the money and actually we are going after the money," he said, adding that the National Crime Agency and Economic Crimes Unit were investigating a wide range of individuals.
"What people want to see is some of the very rich people... whose wealth can be attributed to their relationship with Vladimir Putin, it may be that the law agencies, that the police will be able to put unexplained wealth orders on them, to bring them to justice for their acts of gross corruption," he said.
Mr Johnson also said he had been heartened by strong expressions of support from the US and other allies.
US Ambassador to the United Nations Nikki Haley said on Wednesday that Washington believed Moscow was responsible for the attack, adding it was a crime worthy of UN Security Council action.
Reuters / Newshub.