"French investigators are in the process of investigating our Paris offices," a Lafarge spokeswoman told AFP, confirming a report to that effect of France Inter radio.
"We are cooperating fully with investigators, but we cannot make any further comment on this ongoing inquiry," she said.
A source close to the case said Belgian police were conducting a similar search at the offices of one of Lafarge's subsidiaries in Brussels.
Since June, three French judges have been investigating reported money transfers by Lafarge to groups in Syria, including IS. The 2013 and 2014 transfers allegedly kept operations up and running at its Jalabiya cement works in northern Syria, despite the conflict engulfing the country.
Lafarge clung on in Syria for two years after most French companies had left as IS made major territorial gains, extending its influence over vast swathes of the country. IS eventually took over the Jalabiya plant in September 2014.
To ensure protection of its staff between 2013 and 2014, Lafarge Cement Syria paid between $80,000 and $100,000 a month to various armed groups, including $20,000 to IS, according to a source close to the year-old investigation first revealed last year by French daily Le Monde.
Weeks after the story broke with Le Monde saying Lafarge in Paris knew of the reported arrangements, the French treasury opened an investigation.
Lafarge, which in 2015 merged with Swiss counterpart Holcim, has already admitted to "unacceptable mistakes committed in Syria".
A report by the French national customs judicial department, seen by AFP, has concluded that the company "made payments to jihadist groups" to allow the plant to stay on stream.
The report goes on to say that the firm validated the transactions using false accounting documents.
The European Centre for Constitutional and Human Rights (ECCHR) and French anti-corruption association Sherpa sued Lafarge last year. The lawsuit alleged that the company's payments to IS could constitute complicity in crimes against humanity. Sherpa has called for former French foreign minister Laurent Fabius to be questioned over the payment.