Britain and Russia Brace for Showdown as Deadline Expires for Nerve Attack Explanation

Members of the emergency services wearing protective clothing work next to a children's play area near the bench where former Russian intelligence officer Sergei Skripal and his daughter Yulia were found poisoned in Salisbury, Britain, March 13, 2018. Reuters/Henry Nicholls

LONDON—Britain braced for a showdown with Russia on Wednesday after a midnight deadline set by Prime Minister Theresa May expired without an explanation from Moscow about how a Soviet-era nerve toxin was used to strike down a former Russian double agent.

The United States, European Union, and NATO supported Britain after May said it was “highly likely” that Russia was behind the poisoning of Sergei Skripal and his daughter with Novichok, a nerve agent developed by the Soviet military.