The incident occurred at the Zaisan outlet in Ulaanbaatar last week due to its contaminated water supply, the city's Metropolitan Professional Inspection Agency said, adding that 247 people had reported symptoms such as diarrhea and vomiting.

The Zaisan restaurant has already been shut for checks, an official at the agency told Reuters on Tuesday.

"We will carry out inspections for the other KFC branches from Feb. 18-21 and suspend their operations when we do the inspections," the official added. The regulator had previously said it had suspended all the local KFC outlets.

KFC, which is part of Yum Brands Inc, has at least 11 restaurants in the country, according to its website.

Ganbat Danzanbaatar, general manager of KFC Mongolia, said apart from the Zaisan outlet, all KFC restaurants were open.

KFC opened its first restaurant in Mongolia in 2013 and all its restaurants are 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 KFC Global spokeswoman told Reuters.

"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," she said in an email.

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.