A Japanese drug maker has offered an apology for the widespread health concerns caused by its supplements containing "beni-koji" red yeast rice.

Kobayashi Pharmaceutical on Friday held its first news conference since deaths were reported among users of the products, which are now subject to a recall.

President Kobayashi Akihiro expressed his condolences for the deceased customers and their family members. He added he is deeply sorry for causing concern and anxiety to many people over the issue that has developed into a social problem.

The Osaka-based firm was initially informed of suspected health damage in January, but did not go public for more than two months.

President Kobayashi said the company is seriously reflecting on the severe criticism it has faced over the time lapse, and is deeply remorseful.

The drug maker said that as of Thursday night, there were five deaths and 114 reports of hospitalizations among users of the beni-koji supplements. Those affected are said to have developed kidney problems and other health issues.

Kobayashi Pharmaceutical has launched a probe into what it calls an "unintended substance" that may have gotten into the ingredients of the supplements.

A senior company official said "the structure of the substance" has been coming to light in the past week.

The official said the company will investigate the cause of the health problems jointly with government institutions, by providing data to the government and others.

The health ministry and the agency in charge of consumer affairs have launched a joint Japanese language hotline to respond to inquiries by consumers and businesses.

The number is 03-3595-2760. The call center will operate from 9 a.m. to 9 p.m. every day, including weekends and national holidays.