British Home Secretary Amber Rudd said Thursday will have a plan ready to respond if investigators identify someone responsible for a nerve agent attack against a former Russian double agent.
"There is nothing soft about the UK's response to any sort of state activity in this country," she told the BBC. "You may not hear about it all, but when we do see that there is action to be taken, we will take it."
British counterterrorism police have said Sergei Skripal and his 33-year-old daughter were poisoned by a nerve agent Sunday in the normally quiet town of Salisbury.
A police officer who was part of the initial response to the incident was hospitalized. Rudd said Thursday the officer remained in serious condition but was able to talk.
"This is being treated as a major incident of involving attempted murder by the administration of a nerve agent," Metropolitan Police counterterrorism chief Mark Rowley said. He would not identify the exact substance used or how it was delivered.
The poisoning is threatening a full-scale security and diplomatic crisis for Britain, with lawmakers demanding the government launch an urgent inquiry into more than a dozen recent suspicious deaths in Britain, all potentially tied to Russian intelligence services.
Skripal, 66, and his daughter, Yulia, are fighting for their lives after being found unconscious on a bench outside a shopping mall. Police have been examining CCTV footage and reportedly have focused their attention on a man and woman spotted nearby.
On Tuesday, Britain's foreign minister, Boris Johnson, prompted sharp Russian rebuttals when he assured British lawmakers the government would get to the bottom of the mystery and threatened the imposition of new sanctions on Russia, if the Kremlin were found to have been responsible. Johnson said while he was not pointing the finger at this stage, he described Russia as "a malign and disruptive force."
His remarks were characterized by Russian Foreign Ministry spokeswoman Maria Zakharova as "wild." Russian diplomats in London accused Johnson of "demonizing" their country.
Mark Edele, a Russia analyst at the University of Melbourne in Australia, told VOA investigators may never know who was responsible.
"If Russia is behind this, they will certainly deny it. If they're not behind it, they will also deny it," Edele said. "And the only way to really find out would be to catch whoever did this, which given the level of professionalism involved is probably unlikely."
The incident is drawing comparisons to Alexander Litvinenko, a highly public critic of President Putin and a Russian KGB officer-turned-British intelligence agent, who died agonizingly, days after drinking tea laced with radioactive polonium-210 in a London hotel in 2006. British doctors struggled in that case to identify the substance that killed him.
A British inquiry concluded the Russian leader probably approved the killing. The conclusion was dismissed angrily by the Kremlin as a politically motivated smear.
An eyewitness to the discovery of Skripal and his daughter, Jamie Paine, told British reporters the woman was passed out, frothing at the mouth and her eyes "were wide open, but completely white." He said, "The man went stiff, his arms stopped moving, but he was still looking dead straight." Adding to alarm, one of the emergency service workers who attended the pair has also been hospitalized.
Skripal, who served in Russia's military intelligence agency, GRU, was exchanged in a Cold War-type spy swap in 2010 on the runway at Vienna's airport. After serving four years in prison in Russia for spying for Britain's espionage service, MI6, he was one of four Russian double agents exchanged for 10 Russian sleeper agents expelled from the United States, including Manhattan socialite and diplomat's daughter Anna Chapman.
At the time, Putin, a former KGB officer, issued televised threats against those who had betrayed Russia. "Traitors will kick the bucket. Trust me. These people betrayed their friends, their brothers-in-arms. Whatever they got in exchange for it, those 30 pieces of silver they were given, they will choke on them," he said.
In 2006, a new Russian law was adopted formally permitting extra-judicial killings abroad of people Russian authorities deemed extremist or terrorists, allowing the Russian president alone to order a killing.
Skripal had spied for Britain during the 1990s and continued to communicate with MI6 after his retirement in 1999 from the GRU, while working at the Ministry for Foreign Affairs in Moscow.
Russian prosecutors said Skripal received at least $100,000 for his collaboration with MI6, according to Russian news outlets. At his trial he admitted selling the names, addresses and code names of "several dozen" Russian agents operating in Europe to MI6 over a period of 10 years. British intelligence officials say Skripal identified as many as 300 Russian spies and moles.
A year after the spy swap, he bought a house in Salisbury for $360,000. He lived apparently quietly there with his wife, Lyudmila, until her death from cancer five years ago. But a relative told BBC Russia, "From the first day, he knew it would end badly, and that he would not be left alone," he said.
As British investigators piece together what happened to Skripal, senior British lawmakers say other suspicious Russia-linked deaths during the past two decades need to be re-examined.
Among them: former oligarch Boris Berezovsky; Scot Young, a businessman impaled on an iron fence after a fall from a window; Badri Patarkatsishvili, a Georgian oligarch who died of an apparent heart attack in 2008; Yuri Golubev, an outspoken Putin critic, and Alexander Perepilichny, who fled Russia for London and gave evidence of high-level corruption to Swiss authorities.
VOA's Jamie Dettmer, Victor Beattie and Chris Hannas contributed to this report.