French-based cement giant Lafarge was dealt a blow on Wednesday as a Paris appeals court upheld charges of "complicity in crimes against humanity" in Syria, which have been weighing on the company for years.

A legal adviser for the European Center for Constitutional and Human Rights (ECCHR), which is a party to the case, told Reuters the Paris court of Appeals confirmed a ruling by France's highest court, which last year said Lafarge can be probed for charges linked to crimes against humanity for keeping a factory running in Syria after conflict erupted in 2011.

The decision, another procedural step in a complex investigation, is not a final verdict on the crimes as such.

The investigation into Lafarge, now part of Switzerland-listed Holcim, is one of the most extensive and complex corporate criminal proceedings in contemporary French legal history.

In 2021, Lafarge lost a bid to dismiss the charge of complicity in crimes against humanity in Syria's conflict when France's highest court said the matter should be re-examined, overturning an earlier ruling.

The company has previously admitted, following its own internal investigation, that its Syrian subsidiary paid armed groups to help protect staff at the plant.

But it has rejected several charges against it as part of the French legal probe, including that it was complicit in crimes against humanity because of its dealings with militant groups in the area, which included Daesh.

Should Lafarge be indicted on the charges, it would set a historic precedent as no French firm has yet been tried in connection with crimes against humanity.

Holcim shares were down just over 1% in midday trade.