The U.S.

Earlier this month, Sergei Skripal and his adult daughter, Yulia, were found unconscious on a park bench in Salisbury, England. The two had been poisoned with a nerve agent called Novichok, developed by Kremlin scientists several decades ago. They remain in critical condition.

Skripal is Russian. He was arrested in 2006 for passing state secrets to Britain's MI6 and released in 2010 as part of a prisoner swap. He's been living in Britain ever since.

After an investigation, British officials accused the Kremlin of organizing the March 4 attack, which is thought to have exposed as many as 130 people to the nerve agent. At least 50 were treated in a hospital. In a statement to the House of Commons on March 12, Prime Minister Theresa May said it was “highly likely” that Russian officials organized the poisoning.