The US is to impose sanctions on Russia after determining that it used nerve agent against former Russian double agent Sergei Skripal and his daughter, Yulia, in the UK in March.
The move was announced on Wednesday by the US state department.
Sergei and Yulia Skripal were found unconscious on a bench in the city of Salisbury, England, on 4 March.
They were seriously ill but later made a full recovery after spending several weeks in hospital.
Russia has strongly denied playing any role in the attack.
“The United States… determined under the Chemical and Biological Weapons Control and Warfare Elimination Act of 1991(CBW Act) that the government of the Russian Federation has used chemical or biological weapons in violation of international law, or has used lethal chemical or biological weapons against its own nationals,” state department spokeswoman Heather Nauert said in a statement.
The sanctions are to take effect on or around 22 August, she added.
Following the incident, the British government said the military-grade nerve agent Novichok, of a type developed by Russia, had been used in the attack.
Relations between Russia and the West hit a new low. More than 20 countries expelled Russian envoys in solidarity with the UK, including the US. Washington ordered 60 diplomats to leave and closed the Russian consulate general in Seattle.
Three months after the Salisbury attack, two other people fell ill at a house in Amesbury, about eight miles from the city. Dawn Sturgess later died while her partner, Charlie Rowley, spent three weeks recovering in hospital.
After tests, scientists at the UK’s military research lab, Porton Down, found the couple had also been been exposed to Novichok.
Mr Rowley told ITV News he had earlier found a sealed bottle of perfume and gave it to Ms Sturgess, who sprayed the substance on her wrists.