The UK Daily Mail reports investigators have raided McDonald’s offices in Seoul, South Korea after allegations that several children fell ill after eating the U.S. chain.

At least five children have allegedly suffered life-threatening kidney disease as a result of an infection, after being served under-cooked hamburger patties at McDonald’s.

The raid on Wednesday saw the Seoul central district prosecutors’ office confiscated documents and evidence local news reports said.

Investigators also carried out raids at three other companies, including an ingredient supplier.

A spokeswoman at McDonald’s Seoul office confirmed the raid to Reuters, but gave no reason or further details.

In July, a consumer filed a complaint against the U.S. firm, saying her daughter was diagnosed with hemolytic uremic syndrome – also known as hamburger disease – following the consumption of a McDonald’s hamburger last year.

The parent said that the four-year-old girl had been left with irreversible kidney damage.

Complaints were also filed by parents of four more children who became sick after eating McDonald’s burgers.