Russian former double agent, Sergei Skripal and his daughter were poisoned with a military-grade nerve toxin that had been left on the front door of their home in England, British counter-terrorism police said.

After the first known offensive use of a chemical weapon on European soil since World War Two, Britain blamed Russian President, Vladimir Putin, for the attempted assassination and the West has expelled around 130 Russian diplomats.

Russia has denied using Novichok, a nerve agent first developed by the Soviet military, to attack Skripal, and Moscow has said it suspects the British secret services are trying to frame Russia to stoke anti-Russian hysteria.

“We believe the Skripals first came into contact with the nerve agent from their front door,” said Dean Haydon, Britain Senior National Coordinator for Counter-terrorism Policing.

“Specialists have identified the highest concentration of the nerve agent, to date, as being on the front door of the address,” Scotland Yard said in a statement.

Skripal and his 33-year-old daughter, Yulia, have been in a critical condition since being found unconscious on a public bench in the English city of Salisbury on March 4.

A British judge has said they may have suffered permanent brain damage.

The attempted murder of Skripal, a 66-year-old former colonel in Russian military intelligence, who betrayed dozens of Russian agents to Britain’s MI6 spy service, has plunged Moscow’s relations with the West to a new post-Cold War low.

After Britain expelled 23 Russians it said were spies working under diplomatic cover, Russia followed by throwing out 23 British diplomats.

The U.S. and other Western countries, including most member states of the EU and NATO, expelled over 100 diplomats.

British lawmakers launched a new inquiry into money-laundering, sanctions and economic crime on Thursday, with a particular focus on properties bought with so-called “dirty money”.

British Foreign Secretary, Boris Johnson, said the Kremlin had underestimated the Western response to the attack, which also injured a British policeman.

Johnson told an audience of ambassadors in London that 27 countries had now moved to expel Russian diplomats over Moscow’s suspected involvement, which it denies.

“These expulsions represent a moment when a feeling has suddenly crystallised, when years of vexation and provocation have worn the collective patience to breaking point, and when across the world – across three continents – there are countries, who are willing to say enough is enough,” Johnson said.

Putin, who has been dealing with a deadly shopping center fire in Siberia, has yet to respond, though Moscow has threatened to take retaliatory action against the West.