Prosecutors have raided the office of McDonald's Korea in central Seoul following suspicions that the U.S. fast food company used hamburger patties that were not fully cooked.

The Seoul District Prosecutor's Office sent investigators to McDonald's Korea on Tuesday and secured company records.

The raid comes a year and nine months after nine civic groups led by Political Mamas leveled accusations against McDonald's Korea and patty suppliers for violating food sanitation laws and negligence that caused bodily harm.

In July, 2016, McDonald's Korea was accused of covering up defective hamburgers even after receiving a report from patty producers that tainted burgers remained in its stores.

The patties were reported to have contained hemorrhagic coli that caused food poisoning.