A report by French intelligence services blames Syrian President Bashar al-Assads regime for a suspected chemical attack in rebel-held Syria that killed 87 people, Foreign Minister Jean-Marc Ayrault said Wednesday.

He said the analysis of samples taken at the scene of the April 4 attack in Khan Sheikhun showed "there is no doubt that sarin gas was used".

"There is also no doubt about the responsibility of the Syrian regime given the way that the sarin used was produced," Ayrault told journalists after presenting a report compiled by French intelligence services.

"This (production) method bears the regime's hallmarks and allows us to determine its responsibility for this attack," he said.