US chain Pizza Hut's Indonesian operation insisted its restaurants were safe on Tuesday after it was accused of using ingredients up to six months past their expiry date.

The allegations about Pizza Hut and Pizza Hut Delivery in the country, which are run by local company Sarimelati Kencana, were made in a joint investigation by a magazine and the BBC's Indonesia service.

The restaurant chain, which has more than 300 outlets in the archipelago, was accused of using ingredients including puff pastry, vegetable sausage and carbonara sauce when it knew they were past their expiry date.

Expiry dates were extended for between one and six months, the investigation alleged, citing company documents. The practice had been going on for years with the knowledge of top management, it said.

The investigation also accused Japanese noodle chain Marugame Udon of using ingredients past their expiry date at its handful of outlets in Indonesia.

Both Pizza Hut and Marugame Udon have denied the allegations.

Pizza Hut said on Tuesday that some of its restaurants on Indonesia's most populous island of Java had been inspected thoroughly and health authorities found that they met hygiene and sanitation standards.

Stephen J. McCarthy, president director of Sarimelati Kencana, also defended Pizza Hut, saying he was proud of the outlets' kitchens.

"They're the cleanest Pizza Hut in the world. If somebody wants to visit our kitchens, you give me a call, I will personally take you," he said at the weekend.

"We have a great reputation in Indonesia, we expect that not to change and only to get better."

No one is reported to have fallen ill due to eating the expired ingredients at either Pizza Hut or Marugame.

Pizza Hut has been operating for 32 years in Indonesia and employs more than 13,000 workers.

The Pizza Hut and Marugame Udon franchises in the country are ultimately owned by Indonesian food and beverage giant Sriboga Raturaya.