Federal prosecutors have asked Parkland Memorial Hospital not to publicly release certain documents because of an ongoing investigation into "public corruption, money laundering and tax evasion," according to a document released Wednesday.

The letter from the U.S. Attorney's office in Dallas to the Texas Attorney General asks that Parkland withhold records requested by several reporters under the Texas Open Records Act.

The information requested directly relates to a Department of Justice ongoing investigation, the letter said.

"We are currently conducting a criminal investigation which, in broad terms, involves allegations of public corruption, tax evasion and money laundering," the letter said. "As part of that ongoing investigation, we have directed Parkland to preserve and maintain certain records on our behalf."

The letter, dated Aug. 2 and signed by assistant U.S. Attorney Walt Junker, said release of the documents could interfere or prejudice the investigation.

Allison Sands, spokeswoman for the U.S. Attorney's office, said she could not confirm the letter or the investigation.

"We're not going to comment on it," she said.

"Along with companies such as AT&T, American Airlines, Wal-Mart and several others, Parkland Hospital has been asked by the U.S. Attorney for information concerning certain subjects of its investigation," Parkland said in a statement Wednesday. "The U.S. Attorney has asked that we not release any information about its inquiry as that might impede the investigation. We intend to fully comply with the U.S. Attorney's request."

An FBI spokeswoman in Dallas declined to talk about the case.

A contractor named in search warrants for the FBI's ongoing investigation of Dallas County Commissioner John Wiley Price is also a contractor in the $1.25 billion construction project for a new Parkland Hospital.

Wai-Wize, owned by political consultant Willis Johnson, is listed in several county records about the hospital project.

Johnson has not returned calls.

Parkland is the county's public hospital, and Price is the county's longest-serving elected official.

Separately, the federal agency that administers Medicare notified Parkland it is in jeopardy of losing federal funding after an investigation found threats to patient safety.

Parkland has said it is making improvements and hopes to resolve the federal agency's complaints before the funding deadline of Sept. 2.

More: Complete coverage of the federal investigation in Commissioner John Wiley Price