Punitive measures will take effect on or around August 22, the US State Department announced on Wednesday.

The United States has said it would impose new sanctions on Russia after it determined that Moscow had used a nerve agent against a former Russian agent and his daughter in the United Kingdom.

Heather Nauert, US State Department spokeswoman, said in a statement on Wednesday that it had been determined that Russia “has used chemical or biological weapons in violation of international law”.

She said sanctions would take effect on or around August 22, but did not specify the nature of the new punitive measures.

NBC, a US news network, cited a senior state department official as saying that the sanctions would be structured in two tranches.

The biggest effect from the initial sanctions are expected to come from a ban on granting licenses to export sensitive national security goods to Russia, the report said.

Washington had already expelled dozens of Russian diplomats from the US over the poisoning.

Novichok

Sergei Skripal and his daughter, Yulia Skripal, are believed to have been exposed to the nerve agent Novichok in the British town of Salisbury in March.

They were found slumped unconscious on a park bench and spent weeks in hospital before they were finally released.

Sergei and Yulia Skripal were attacked with a nerve agent in Salisbury [Rex Features]

At least two other people were hospitalised after suffering from exposure to the chemical agent, Novichok, in a town near Salisbury.

Charlie Rowley, 45, was released from a hospital last month, but his partner, Dawn Sturgess, 44, died after exposure.

Rowley and Sturgess were hospitalised after being exposed to the deadly nerve agent June 30.

Police found a bottle containing the substance at the scene. Sturgess died in hospital.

Russia denies being behind the poisonings.