Federal investigators searched Tuesday the New England Compounding Center, which supplied drugs tied to the deadly meningitis outbreak.

A spokeswoman for the U.S. Food and Drug Administration said its criminal investigators were at the NECC, based in Framingham, Mass.

They were aided  by with officers from the local police, Framingham police told Reuters.

Carmen Ortiz, U.S. attorney for Massachusetts, said in a statement, "I can confirm that this office and our law enforcement partners are investigating allegations concerning the New England Compounding Center."

Ortiz said it was "entirely premature" to speculate about what might be uncovered.

A lawyer for NECC, said the raid was unnecessary and that "asking would have produced the same result."

"It is difficult to understand the purpose of this search, since we have been clear that (NECC) would provide, and has provided, anything requested. We've been clear that warrants weren't needed," Paul Cirel, of the firm Collora LLP in Boston, said in a statement.

Also on Tuesday, federal health officials updated treatment guidelines for the outbreak, saying oral medicine can be used to treat mild cases of meningitis.

The Centers for Disease Control and Prevention said there is growing evidence that the fungus Exserohilum rostratum, "a brown-black mold," is the predominant pathogen behind the fungal-meningitis outbreak associated with tainted steroid injections made by NECC, The Wall Street Journal reported.

On Monday, health officials said two other medicines made by the company may also be linked to illnesses. As of Tuesday, the CDC said there have been 231 cases of fungal meningitis that have caused 15 deaths. There have also been two joint infections.