NEW YORK (NYTIMES) - The authorities in Valencia, Spain, are investigating the death of a woman who had eaten at a Michelin-starred restaurant, its owner said this week, as Spanish news outlets reported that the establishment had been tied to as many as 28 other cases of food poisoning.

The restaurant, RiFF, has closed indefinitely as regional health officials investigate.

Mr Bernd H. Knoller, the owner and head chef of RiFF, said in a statement that the restaurant would be closed until "the causes of what happened are established and we can resume work with full guarantees for both the staff and customers".

He said the decision was based on what he had learnt from Valencian health authorities about "different gastric illnesses in several customers of the restaurant, including the death of one".

Mr Knoller said he had offered his "full collaboration" with the investigation by the regional Ministry of Health to determine what caused the death.

The woman, who has not been publicly identified by the authorities, died at her home on Sunday (Feb 17) morning, the restaurant said in an e-mailed statement.

"We are awaiting the results of the official investigation, which will determine whether the cause of death has any connection with the food served at the restaurant," it said. "All other guests have recovered from the symptoms."

Valencia's Ministry of Health did not respond to requests for comment. The head of the ministry, Ms Ana Barcelo, told reporters on Thursday (Feb 21) that investigators had interviewed 75 people who had eaten at the restaurant between Feb 13 and Feb 16, according to the Spanish news outlet Europa Press.

Of those 75, investigators found 29 with symptoms of food poisoning, including the woman who died, the Spanish newspaper El Pais reported. The other 28 people were said to have suffered mild symptoms, including vomiting and diarrhoea, it said.

Ms Barcelo declined to comment on speculation that a mushroom might have caused the outbreak, saying it was "irresponsible to establish the origin" before an autopsy and other tests were completed.

She also said an initial inspection of the restaurant found that "everything appears normal", according to El Pais.

Citing anonymous sources within the ministry, the newspaper said the authorities first learnt of food poisoning symptoms on Feb 17, the day after the woman who died had fallen ill, as had her husband and their son.

Ms Barcelo said that the authorities had collected samples from the restaurant's tasting menu for tests by the National Institute of Toxicology and Forensic Science.

RiFF was awarded a star by the prestigious Michelin Guide in 2009, according to the restaurant's website. The guide said the chef, Mr Knoller, created "innovative cuisine" and "interesting set menus" based on "the highest quality, seasonal, local products".