LONDON: Britain will hold new emergency talks Tuesday into the brazen nerve agent poisoning of a Russian former double agent on its soil, after the US and NATO backed London in implicating Moscow in the assassination attempt.
As diplomatic tensions soar, Russia has denied accusations of its involvement in the attack on Sergei Skripal and his daughter in southwest England on March 4.
British Prime Minister Theresa May told parliament it was "highly likely" Moscow was behind the poisoning, giving Russia until the end of Tuesday to answer the accusations, in comments that have stoked speculation Britain could call on its allies to mount a joint response.
Both the United States and NATO issued statements in support of London, as concern mounts over the use of what May described as a military-grade nerve agent developed by Russia.
Skripal, 66, and his daughter Yulia, 33, remain in a critical condition in hospital after being found unconscious on a bench outside a shopping centre in Salisbury.
Emergency workers in biohazard suits have been deployed in the normally sleepy city, while some 500 people who may have come into minimal contact with the nerve agent were urged to wash clothes and belongings as a precaution.
US Secretary of State Rex Tillerson said Washington has "full confidence" in the British investigation, adding that it was "almost beyond comprehension" that a state would use such a dangerous substance on public streets.
"We agree that those responsible -– both those who committed the crime and those who ordered it -– must face appropriately serious consequences," he told reporters.
"We stand in solidarity with our allies in the United Kingdom and will continue to coordinate closely our responses."
- 'Great concern' -
May told British lawmakers that Moscow had previously used the group of nerve agents, known as Novichok, had a history of state-sponsored assassinations and viewed defectors such as Skripal as legitimate targets.
"The government has concluded that it is highly likely that Russia was responsible for the act against Sergei and Yulia Skripal," she said.
The prime minister added Britain had given Moscow until the end of Tuesday to disclose details of its development of the Novichok nerve agents programme to the Organisation for the Prohibition of Chemical Weapons.
If there was "no credible response" it will conclude it was "an unlawful use of force by the Russian State against the UK", she warned, and pledged to outline a "full range of measures" in response on Wednesday.
The Daily Telegraph newspaper reported on Tuesday that Britain was consulting allies in NATO about possibly invoking its Article 5 principle of common defence.
NATO Secretary General Jens Stoltenberg said the incident was "of great concern" to the alliance.
"NATO is in touch with the UK authorities on this issue," he added in a statement issued by his office Monday.
Russian President Vladimir Putin brushed aside questions about Moscow's involvement in the attack in Britain, telling the BBC: "First get to the bottom of it there and then we will discuss this."
Earlier Monday, Moscow rejected May's assertions, saying it was "a circus show" and an attempt to undermine trust ahead of its hosting of this summer's football World Cup.
The prime minister's statement was part of "another information and political campaign based on provocation," said Russian foreign ministry spokeswoman Maria Zakharova in comments carried by news agencies.
Meanwhile, French President Emmanuel Macron "offered his solidarity with the UK" in a phone call with May.
"They discussed the wide pattern of aggressive Russian behaviour and agreed that it would be important to continue to act in concert with allies to address it," Downing Street said.
Britain's home secretary Amber Rudd will chair a meeting of the government's emergency Cobra committee at 11:30 am (1130 GMT) Tuesday for an update on the investigation, the Home Office said.
- 'Sophisticated' poison -
Skripal, an ex-military intelligence officer who was jailed for selling Russian secrets to London, moved to Britain in a spy swap in 2010, settling in Salisbury.
Police are investigating the attack against him with the assistance of Britain's armed forces and its military research laboratory at Porton Down.
Pharmacology experts said Novichok, a broad category of more than 100 nerve agents developed by Russia during the late stages of the Cold War, was "more dangerous and sophisticated" than sarin or VX.
"It causes a slowing of the heart and restriction of the airways, leading to death by asphyxiation," said Gary Stephens, a professor at Britain's University of Reading.
Britain had voiced its concerns about Russia still having such biological weapons during a 2008 meeting in Paris of countries to discuss such threats, according to WikiLeaks cables reposted on Twitter Monday.
The BBC reported that investigators now believe the nerve agent may have been deployed in powder form through the ventilation system of Skripal's car.
Other reports in the British media hinted at growing pressure on May for England to boycott this summer's World Cup in Russia.
"How can we go to Putin's World Cup now" read the headline of the Daily Mail.