The US is to impose sanctions on Russia after determining that it used the nerve agent Novichok 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 town of Salisbury, England, on 4 March.
They were seriously ill but later made a full recovery after spending several weeks in hospital.
In June Dawn Sturgess and Charlie Rowley were also exposed Novichok. Dawn Sturgess, 44, died in hospital after falling critically ill on 30 June.
Charlie Rowley, 45, who was also exposed to the nerve agent in Amesbury, became critically but made a recovery.
“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 Skripal’s incident, the British government said the military-grade nerve agent Novichok, of a type developed by Russia, had been used in the attack.
After tests, scientists at the UK’s military research lab, Porton Down, found Dawn Sturgess and Charlie Rowley 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.