UK police believe former Russian spy Sergei Skripal and his daughter were poisoned by a nerve agent over the weekend.
At a press conference on Wednesday, Metropolitan Police Assistant Commissioner Mark Rowley said police were treating the incident as "attempted murder by a nerve agent." He added that police believe the couple were specifically targeted.
Sergei Skripal -- a former Russian military official convicted of spying for the UK -- and his daughter Yulia are critically ill in a UK hospital after passing out on a shopping center bench in the southern English town of Salisbury on Sunday.
Rowley said that a police officer who had arrived to the scene had also fallen ill and was now in serious condition in hospital.
The counterterrorism unit of London's Metropolitan Police has taken over the investigation from local police.