Swallow said in a statement Friday that he is happy the U.S. attorney is investigating "the baseless allegations against me."
"In calling for the investigation last week, I said I would cooperate fully with a swift and fair investigation. I am eager to expose the truth about the false and defamatory allegations made against me," Swallow said
Former U.S. Attorney Brett Tolman said that the allegations surrounding Swallow present a unique situation for the state's top federal prosecutor.
"I think when there are circumstances like this where it's a sitting attorney general in the state and the whole state is wondering, 'Is anyone looking into this? Is anything being done?' It's an appropriate exception to the policy that you don't confirm or deny the existence of an investigation," Tolman said.
The statement does not say when the investigation began, and sources had told The Salt Lake Tribune last month that they had already been interviewed about indicted businessman Jeremy Johnson's relationship with Swallow, among other issues.
Swallow, on Jan. 14, asked U.S. Attorney David Barlow to conduct an investigation into the allegations by Johnson that Swallow had helped broker a bribe to enlist Senate Majority Leader Harry Reid, D-Nev., to help derail a Federal Trade Commission investigation into Johnson's businesses.
Swallow has denied any such scheme, saying he merely helped Johnson hire lobbyists to work on his case. Reid's office has said the senator has no knowledge of the matter.
Typically, investigations into elected officials are coordinated with the Public Integrity Section in Washington, D.C.
Utah Democrats praised the U.S. attorney for taking the matter seriously.
"It has always been our position that the serious nature of these accusations against Attorney General Swallow demand a serious, impartial, non-Utah investigation to follow the facts, wherever they may lead," Utah Democratic Party Chairman Jim Dabakis said in a statement.
Gov. Gary Herbert said Thursday that people should await the results of the federal investigation before judging Swallow.
His comments came the day after Utah Republican Party Chairman Thomas Wright said that Swallow had made "mistakes" in judgment in his dealings with Johnson.
Both Wright and Herbert called for changes to the state's ethics laws regarding elected officials, including an ethics commission which does not exist now to hear complaints against state officers and restrictions on outside consulting work by state employees.