The French foreign minister has said a UN report into a chemical attack in Syria leaves no doubt about the responsibility of President Bashar al-Assad's government.

Laurent Fabius said: "When you look at the amount of sarin gas used, the vectors, the techniques behind such an attack, as well as other aspects, it seems to leave no doubt that the (Assad) regime is behind it."

Mr Fabius was speaking after a meeting with his Russian counterpart Sergei Lavrov in Moscow.

Mr Lavrov said Russia has "very serious grounds" to believe the 21 August chemical attack was a provocation.

He also said the UN report does not answer all Russia’s questions about the attack.

UN inspectors have confirmed they found "clear and convincing evidence" that poison sarin gas was used in the attack near Damascus.

The UN team's mandate was solely to determine whether chemical weapons were used, not who used them.

However, a reference to surface-to-surface rockets may point to government use rather than its lesser-armed opposition.

During a visit to a site at Moadamiyah where a number of people were said to have died in a chemical attack, UN inspectors recovered munitions fragments marked with numbers and engraving, although no debris was recovered intact.

The report said the site had been well travelled by other individuals prior to the arrival of inspectors.

It said fragments and other possible evidence had clearly been handled or moved.