UK Deepens Investigation Into Possible Poisoning Of Former Russian Spy In England

Britain has stepped up its investigation into the possible poisoning of former Russian spySergei Skripal in Salisbury, England, with the U.K. government facing the possibility ofyet another Russian dissident being assassinatedon British soil.

On Sunday, 66-year-old Sergei Skripal, a former colonel in the Russian military intelligence, wasfound unconsciouson a bench at a mall in Salisbury, along with his 33-year-old daughter, Yulia. As of Tuesday, the two were still in critical condition, being treated “forsuspected exposure to an unknown substance.”

Skripal was sentenced to prison by Russia in 2006 for spying for Britain. In 2010 he was given refuge in the U.K. as part of a “spy swap” with the United States.

Britain’s counterterrorism unit took over the investigation Tuesdayfrom local law enforcement because of its “unusual circumstances.”Samples from the scene were being testedat a military research laboratory, The Guardian reported. The police had not declared it a terrorist incident, and law enforcement officials werestill investigatingwhether a crime occurred.

British Foreign Secretary Boris Johnson said Tuesday that, although it was “too early to speculate” about what happened to Skripal and his daughter, Britain would “respond appropriately and robustly” if the Russian government were found to be responsible, the Press Association reported. The Kremlin has denied having any information about the incident.

If the incident is found to be a poisoning attempt by the Russians, it would join a longhistory of suspected assassinationsofRussian dissidents abroad, andspecifically in the U.K.

The incident has recalled thehigh-profile assassination in 2006 of another Russian spy, former KGB officer Alexander Litvinenko, poisoned in London. A 2016 inquiry by the British government found Russian agency FSB (which succeeded the KGB) had Litvinenko killed in anoperation “probably approved” by Russian President Vladimir Putin. The Kremlin has repeatedly denied involvement.

Though police said there was no threat to the wider public,nearby restaurant Zizzi and pub The Bishop’s Mill have been cordoned offby police.Severalemergency service personnel who went to the scene were assessed at the hospital, andone remained hospitalized Tuesday, Wiltshire police said.

This article originally appeared on HuffPost.