Lafarge pleaded guilty in a US court Tuesday to paying millions of dollars to the Islamic State group and other jihadists in war-torn Syria between 2013 and 2014, and agreed to a $778 million fine over conspiring to provide material support to US-designated "foreign terrorist organisations".

The US Justice Department said company executives, including former chief Bruno Lafont, knew of the arrangement with the jihadists.

After the settlement, Lafarge now faces the possibility of the introduction of evidence from the US prosecution into a separate French case over similar charges.

Lafont -- who was chief executive from 2007 to 2015, when the company merged with the Swiss building supplies company Holcim -- again strongly denied "ever being informed of any payments to the benefit of terrorist groups or any provision of supplies to such groups", according to a statement issued through his lawyers.

The former chief, who has been charged with "financing a terrorist organisation" in the French case, accused Holcim of singling him out for blame.

"It appears throughout the testimonies and revelations of those involved in this case that the so-called inquiry led by Holcim is entirely and exclusively biased against Bruno Lafont and the former directors of the Lafarge group, and that Holcim has systematically been opposed to finding out the truth," the statement said.

"This raises questions about the facts and responsibilities that Lafarge admitted to in the United States under Holcim's guidance."

Holcim, which says it took over Lafarge without knowledge of the Syria business dealings, said it had been cleared of any wrongdoing by US authorities.

Lafont said he wished to again appear before French investigating magistrates to "touch on certain recent elements" and "request the declassification of certain documents", and is also seeking "the testimony of certain people likely to add new elements on the case".

Lafarge still faces charges in France of complicity in crimes against humanity over the dealings to keep open the Jalabiyeh cement plant in northern Syria.

In May, a French appeals court approved the charge, opening the door for a trial of the company and eight former executives, including Lafont.

Unlike in the United States, the group does not have the option of negotiating a settlement, which is not allowed under French anti-terrorism statutes.