France’s foreign ministry has said it is “very likely” that proof has disappeared from the location of a suspected poison gas attack in Syria, adding it was essential that international inspectors be given full access to the site.

Inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) travelled to Syria last week to inspect the site, but did not gain access to Douma, which is now under government control after revel forces withdrew, until Tuesday afternoon.

“It is very likely that proof and essential elements are disappearing from this site,” the foreign ministry said in a statement.

It follows a row between the US and UK, on one hand, and Moscow on the other, over inspectors’ access to Douma.

Theresa May has accused Russia of blocking the OPCW from travelling to the area, while Kenneth Ward, the US envoy to the body, voiced fears the location may have been tampered with.

Russia’s foreign minister, Sergei Lavrov, strongly denied any tampering had taken place while other Russian officials said inspectors had not been able to visit Douma because of Saturday’s air strikes, and because they lacked the correct permits.

“I can guarantee that Russia has not tampered with the site,” Mr Lavrov told the BBC.

France, the UK and the US hit Syria with retaliatory air strikes after blaming Bashar al-Assad‘s regime for the alleged chemical attack in Douma on 7 April.

Both Ms May and Emmanuel Macron have faced criticism over the action, with MPs in Britain preparing for a second Commons debate on the issue this afternoon.