A Massachusetts pharmaceutical factory was searched by Criminal investigators from the US Food and Drug Administration, which made tainted drugs that has killed 15 people.
The search comes a day after the FDA identified two new drugs produced by the New England Compounding Center (NECC) which may have infected patients with a rare form of fungal meningitis.
"This is part of our ongoing investigation... to fully investigate the scope and cause of the outbreak of fungal meningitis," Sara Clark-Lynn, a spokeswoman for the FDA, told AFP.
But the Boston Globe published pictures on its website of agents with blue jackets bearing the yellow letters "FDA OCI" -- which stands for the FDA's Office of Criminal Investigations -- standing outside NECC's brick office building.
The widening outbreak has led to calls for tighter regulation of the loosely controlled pharmaceutical compounding industry.
Critics said drug manufacturers have found a way to sidestep costly and strict oversight by classifying themselves as pharmacies, which are given freer rein to mix drug compounds for patients.
Some 14,000 people in 23 states were exposed after at least three lots of a steroid produced by NECC were contaminated with fungus. The drug is commonly injected into the spine to treat back pain.
The FDA has not yet determined how many people are at risk of contracting the infection from other potentially tainted NECC drugs, but said the sterility of the facility's products is "of significant concern."
The number of cases rose to 233 in 15 states Tuesday, including two cases of "peripheral joint infection," according to the latest tally by the Centers for Disease Control and Prevention.
Health officials have warned it could be weeks or even months before authorities have a final tally of the infections, due to the deadly fungal infection's long incubation period.