Mongolia has temporarily suspended operations of all KFC restaurants in the country to conduct an inquiry, as 42 people were hospitalized and hundreds showed food poisoning symptoms after eating at one of the outlets of the fast-food chain.

The incident occurred in Ulaanbaatar last week and was caused by poor internal hygiene checks, the city’s Metropolitan Professional Inspection Agency said, adding that 247 people had reported food poisoning symptoms such as diarrhea and vomiting.

Preliminary checks show it was caused by the restaurant’s water supply where bacteria had bred, the agency said on Monday.

KFC, which is part of Yum Brands Inc, opened its first restaurant in Mongolia in 2013 and currently has 11 restaurants there, all in the capital. They are operated by its franchise partner, Mongolian conglomerate Tavan Bogd Group.

“We deeply regret the negative impact that many people have suffered, especially to our guests of the Zaisan restaurant, and we are working to support our team members and customers during this difficult time,” a spokeswoman for KFC Global told Reuters in an e-mail on Tuesday.

“KFC Mongolia is cooperating fully with the government’s investigation and recommendations around addressing the source of the incident. This includes a thorough investigation of all KFC Mongolia restaurants, and specifically into determining the exact cause of the reported incident.”

Tavan Bogd apologized in a separate statement, saying the incident had happened due to weak internal quality checks and that daily standards and rules were poorly implemented.