THE US has reportedly said Russia used a chemical weapon to try to assassinate ex-spy Sergei Skripal in Britain, and it is to impose new sanctions.

Secretary of State Mike Pompeo has signed off on a determination that Russia violated international law by poisoning the former spy, Sergei Skripal, and his daughter, Yulia, in March, the officials said.

The Skripals spent several weeks in hospital after falling seriously ill.

State department spokeswoman Heather Nauert said: “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.”

She said the sanctions will take effect on or around August 22.

The new sanctions, details of which were not immediately released, were to take effect following a 15-day Congressional notification period, she said.

The action follows the US Treasury’s imposition of sanctions in March against 19 Russian citizens and five entities for interfering in the 2016 US election - the toughest steps against Moscow since MR Trump took office.

They came after the US intelligence community’s conclusion that Russia tried to help Mr Trump win the 2016 presidential race.

The new announcement could bolster Mr Trump’s claim that his administration is taking a tough stance on Moscow, even as he denounces special counsel’s Robert Mueller’s Russia probe as a “witch hunt” that ought to be halted immediately.

Mr Trump caught flak from Democrats and Republicans alike for what many saw as his unsettling embrace of Mr Putin last month at their Helsinki summit, when Mr Trump appeared to disavow his own intelligence agencies’ assessment on Moscow’s election interference.

Sergei and Yulia Skripal were found unconscious on a bench in Salisbury, England, on March 4, having been poisoned by Novichok, a military-grade nerve agent developed by the Soviet Union during the Cold War.

They were critically ill, but survived after spending weeks in the hospital. Russia has strongly denied playing a role in the attack.

On June 30, a British couple were poisoned by Novichok in a nearby town - 44-year-old mother-of-three Dawn Sturgess subsequently died while her boyfriend Charlie Rowley recovered.

London and its allies have accused Moscow of trying to kill the Skripals and says the two cases are likely linked.