PARIS — France’s foreign minister said Wednesday that the chemical analysis of samples taken from a deadly sarin gas attack in Syria earlier this month “bears the signature” of President Bashar al-Assad’s government and shows it was responsible for the deadly assault.

According to Foreign Minister Jean-Marc Ayrault, France came to this conclusion after comparing samples from a sarin attack in Syria from 2013 that matched. The findings came in a report published Wednesday.

The Kremlin promptly denounced the French report, saying the samples and the fact the nerve agent was used are not enough to prove who was behind it.

France knows “from sure sources” that “the manufacturing process of the sarin that was sampled is typical of the method developed in Syrian laboratories,” Ayrault added. “This method bears the signature of the regime and that is what allows us to establish its responsibility in this attack.”

France’s Foreign Ministry said blood samples were taken from a victim in Syria on the day of the April 4 attack in the opposition-held town of Khan Sheikhoun in which more than 80 people were killed.

Environmental samples, the French ministry said, show the weapons were made “according to the same production process [as] the one used in the sarin attack perpetrated by the Syrian regime in Sarabeq.”

France’s presidency said the country’s intelligence services presented evidence which “demonstrate that the (Syrian) regime still holds chemical warfare agents, in violation of the commitments to eliminate them that it took in 2013.” It says the information will be made public.

It’s thought that Assad’s government still has a stockpile of hundreds of tons of chemical weapons despite saying it had handed over all of them.

Speaking to reporters in Moscow, Kremlin spokesman Dmitry Peskov said Russia’s position on the attack is “unchanged” and that “the only way to establish the truth about what happened near Idlib is an impartial international investigation.”

Russia has previously urged an international probe, and Peskov expressed regret that the Organization for the Prohibition of Chemical Weapons has turned down the Syrian government’s offers to visit the site of the attack and investigate.

The United States has also blamed Assad’s government for the April 4 attack in Khan Sheikhoun. The Trump administration fired cruise missiles at a Syrian air base in retaliation for the attack and issued sanctions on 271 people linked to the Syrian agency said to be responsible for producing non-conventional weapons. Syria has strongly denied the accusations.

Earlier Wednesday, Russian Foreign Minister Sergey Lavrov said the airstrike that the US launched at a Syrian military base in retaliation for the Khan Sheikhoun attack damaged the prospects of a political settlement for the war-torn country.

Lavrov told a security conference in Moscow the US response “pushes the prospect for a wide international front on terror even further away.”

Defense Minister Sergei Shoigu said Russia had to boost security measures at its air base in Syria after the US airstrike. Russia has provided air cover for the government’s offensive on Islamic State militants.