The United States has imposed sanctions on seven senior Russians as it said its intelligence concluded that Moscow was behind the poisoning of jailed Kremlin critic Alexei Navalny.
In action coordinated with the EU, the United States renewed demands that Russia free Navalny, who was arrested in January upon his return to Moscow as he spurred massive rallies through his allegations of corruption by President Vladimir Putin.
"The intelligence community assesses with high confidence that officers of Russia's Federal Security Service FSB used a nerve agent known as Novichok to poison Russian opposition leader Alexei Navalny on August 20, 2020," a senior US official said.
Officials said that the United States would impose sanctions on "seven senior members of the Russian government" with the details expected to be released later today.
They also said that the US would restrict exports to Russia as it vowed that President Joe Biden would take a harder line than his predecessor Donald Trump, who voiced admiration for Mr Putin.
"The United States is neither seeking to reset our relations with Russia, nor are we seeking to escalate," one official said.
"We believe that the United States and our partners must be clear and impose costs when Russia's behaviour crosses boundaries that are respected by responsible nations, and we believe there should be guard rails on how these adversarial aspects of our relationship play out," the official said.
Navalny fell violently ill when he was on a domestic flight last year.
He was taken to Germany for treatment where doctors said he had been poisoned with Novichok, a nerve agent developed by Soviet researchers and which was also blamed in a 2018 attack in England against Russian double-agent Sergei Skripal and his daughter and Yulia.
In a court ruling last month, Navalny was sentenced to three-and-a-half years in prison for breaching the terms of his parole under a 2014 suspended sentence on fraud charges, because he did not check in with the prison service while in Germany.
The judge in his case said time Navalny previously spent under house arrest in the sentence would count as time served.
He has since been transferred to a penal colony.
Russian Foreign Minister Sergei Lavrov has said that Moscow would respond in kind to any new US sanctions
The Kremlin has denied any role in Navalny's illness and said it had seen no proof he was poisoned.