The U.K.'s foreign secretary warned of a "robust" response if it's proven Russia was behind a former spy's sudden collapse and serious illness.
Boris Johnson suggested the U.K. wouldn't participate in the upcoming soccer World Cup, which Russia is hosting.
News outlets report Sergei Skripal, a former Russian intelligence officer, and a woman reported to be his daughter were hospitalized in England after "suspected exposure to an unknown substance." Both are currently in critical condition.
The U.K.'s counterterrorism unit is heading up the investigation. The incident is already being compared to the alleged assassination of Alexander Litvinenko, a former K.G.B. officer who died after being exposed to a rare radioactive isotope.
A British investigation found Litvinenko was exposed following a meeting with Russian associates at a hotel, and authorities determined Russian leader Vladimir Putin "probably" ordered the hit.