The nerve agent that killed a woman in Amesbury, Wiltshire was the same one used to poison the former Russian spy Sergei Skripal and his daughter, Yulia, in Salisbury, the international chemical weapons watchdog has confirmed.

Dawn Sturgess and her partner, Charlie Rowley, fell ill on 30 June after coming into contact with the chemical. Both Sturgess, 44, and Rowley, 45, were treated in hospital and mother-of-three Sturgess died just over a week later.

Quick guide What is novichok? Show Hide Novichok refers to a group of nerve agents developed by the Soviet Union in the 1970s and 80s to elude international restrictions on chemical weapons. Like other nerve agents, they are organophosphate compounds, but the chemicals used to make them, and their final structures, are considered classified in the UK, the US and other countries. The most potent of the novichok substances are considered to be more lethal than VX, the most deadly of the familiar nerve agents, which include sarin, tabun and soman. Novichok agents work in a similar way, by massively over-stimulating muscles and glands. Treatment for novichok exposure would be the same as for other nerve agents, namely with atropine, diazepam and potentially drugs called oximes. The chemical structures of novichok agents were made public in 2008 by Vil Mirzayanov, a former Russian scientist living in the US, but the structures have never been publicly confirmed. It is thought they can be made in different forms, including as a dust aerosol. The novichoks are known as binary agents because they only become lethal after mixing two otherwise harmless components. According to Mirzayanov, they are 10 to 100 times more toxic than conventional nerve agents. Photograph: Matt Cardy/Getty Images Europe

The UK government concluded in July that the substance was the same military-grade novichok nerve agent previously used on the Skripals four months earlier, in an attack that also left Wiltshire police officer Nicholas Bailey seriously unwell, and laid the blame for the attack on the Russian state. The Organisation for the Prohibition of Chemical Weapons (OPCW) has now confirmed this, after twice sending experts to the UK.

“The results of the analysis by the OPCW-designated laboratories of environmental and biomedical samples collected by the OPCW team confirm the findings of the United Kingdom relating to the identity of the toxic chemical that intoxicated two individuals in Amesbury and resulted in one fatality,” the organisation said on Tuesday.

“The toxic chemical compound displays the same toxic properties of a nerve agent. It is also the same toxic chemical that was found in the biomedical and environmental samples relating to the poisoning of Mr Sergei Skripal, Ms Yulia Skripal, and Mr Nicholas Bailey on 4 March 2018 in Salisbury.”

Rowley, 45, was discharged in July but was later readmitted to Salisbury district hospital. It recently transpired he is being treated for meningitis and sight problems.

The hospital said on Tuesday it would not talk about individual cases, adding: “To reiterate what we have said previously, we are not currently treating anyone for nerve agent-related illnesses.”

When Rowley was discharged from hospital, health chiefs made it clear he had been decontaminated. He is said to now be on a ward with six other people, suggesting doctors do not believe he is still suffering from the effects of novichok.

The foreign secretary, Jeremy Hunt, released a statement in response to the OPCW’s finding. “The recklessness of the Russian state in bringing a nerve agent into the UK, and total disregard for the safety of the public, is appalling and irresponsible. Our thoughts are with the family of Dawn Sturgess, and with Charlie Rowley,” he said.

“This is another reminder of the importance of the international community standing together to uphold the global ban on all use of chemical weapons, and ensure that the rules-based international order is respected so we can all keep our citizens safe.”