Former Lafarge CEO Bruno Lafont was questioned on Wednesday over allegations that the French cement-maker indirectly financed jihadists in Syria, sources close to the case said.

Lafont was questioned along with former human resources chief Eric Olsen and former deputy managing director for operations Christian Herrault, the sources told AFP.

Lafarge is accused of paying the Islamic State group and other militants through a middleman so that the company's factory in Jalabiya, northern Syria, could continue to operate in a war zone.

Lafont headed Lafarge from 2006 to 2015, when the company merged with the Swiss building supplies company Holcim, before serving as co-chairman of LafargeHolcim until April this year.