Sanctions have been imposed on seven Russian nationals accused of involvement in the nerve agent poisoning of a key Kremlin critic, the Government said.

The Foreign, Commonwealth and Development Office (FCDO) announced the individuals, said to be members of the Russian Federal Security Service, would be subject to travel bans and asset freezes.

The department added it believes the sanctioned individuals were “directly responsible” for planning or carrying out the attack on Russian opposition leader Alexei Navalny on August 20 2020.

Foreign Secretary Dominic Raab said: “Since the horrific poisoning of Alexei Navalny took place a year ago, the UK has been at the forefront of the international response against this appalling act.

“Through our chemical weapons sanctions regime and at the Organisation for the Prohibition of Chemical Weapons, we are sending a clear message that any use of chemical weapons by the Russian state violates international law, and a transparent criminal investigation must be held. We urge Russia to declare its full stock of Novichok nerve agents.”

Mr Navalny, one of Russian president Vladimir Putin’s most vocal critics, was arrested on January 17 after returning from Germany, where he spent months recovering from the Novichok poisoning.

The anti-corruption investigator blames the Kremlin for targeting him with the nerve agent.

The UK previously imposed sanctions on six Russians, including the director of the Federal Security Service, who the Government holds responsible for the poisoning.

We continue to underline that there must be accountability and no impunity for those that use chemical weapons

Imprisoned Mr Navalny marked the anniversary of the poisoning attack against him by urging global leaders to put more attention on combating corruption and to target tycoons close to Mr Putin.

The UK and United States also issued a joint statement in which they reaffirmed their condemnation of the “assassination attempt” on Mr Navalny.

The statement added: “We welcome sanctions actions made by international partners and will continue to co-ordinate with international partners on further measures.

“Today the UK and the US join in taking further action against the individuals directly responsible for carrying out the poisoning of Mr Navalny.

“As we did after Russia’s use of a chemical weapon against the Skripals in the United Kingdom in March 2018, we continue to underline that there must be accountability and no impunity for those that use chemical weapons.”