Ezzsteel, Egypt's largest steel maker, said on Wednesday its plants were operating although not at full capacity and said an investigation involving the chairman would not affect company activity.

"Ezzsteel's plants are operating and have not suffered any physical damage. The plants are not currently operating at full capacity due to the logistical impact of the government imposed curfew and disruption of communications," it said.

The firm said in a statement that it understood its 7,000 staff were safe and unharmed. It said one of its corporate offices in Cairo was looted and damaged in unrest.

"The company confirms that ... Ahmed Ezz, Ezzsteel's Chairman and major shareholder, has been directed by the Egyptian authorities to remain in Egypt. This measure, which is strictly personal to Ezz, does not affect the operation of the company," it said, adding Ezz was in Cairo.

It also said Ezz, who had held a senior position in the ruling party, "strongly denied" allegations levelled at him regarding vote rigging in the November parliamentary election.