WASHINGTON (AP)--Federal health officials on Wednesday rebuffed a U.S. lawmaker's attempt to meet with a Food and Drug Administration special agent who is investigating an antibiotic linked to a dozen reports of liver failure, including several deaths.

Sen. Chuck Grassley, R-Iowa, said Health and Human Services Department officials denied him access to the agent. Grassley later said he may convene a Senate Finance Committee hearing as part of that staff's ongoing investigation into allegations of fraud connected with trials of the drug, Ketek.

"I smell a cover-up," said Grassley, who is chairman of the committee.

Allowing the agent to speak to Grassley would have violated policy and compromised that agent's work, FDA spokeswoman Susan Bro said.

"Imposing inquiries on an investigator during the process and or releasing documents involved with an open investigation could essentially provide a roadmap of our ongoing work and seriously undermine the investigation," Bro said.

The FDA has received reports of 12 cases of acute liver failure, including four deaths, in patients treated with Ketek, according to an internal FDA memo. Sanofi-Aventis SA (SNY) makes the drug, which the FDA approved in 2004. The company has said it believes Ketek is safe and effective when used as directed.

If warranted, the FDA would consider strengthening warnings on the drug's label, Bro said.

The FDA-approved label for Ketek warns of liver disfunction that can be severe but is "usually reversible."