Deputy Attorney General Rod Rosenstein on Wednesday refused to describe to House lawmakers the scope of special counsel Robert Mueller's Russia investigation, but did say the scope has been "clarified" along the way, and hinted it may have been expanded in certain ways.

Rep. Lamar Smith, R-Texas, said in a House Judiciary Committee hearing with Rosenstein that he's worried Mueller's probe is going far beyond questions related to whether Russia conspired with the Trump campaign to turn the 2016 election against Hillary Clinton.

In response to a question from Smith, Rosenstein indicated that he must authorize any request from Mueller to expand his probe.

"I know what he's doing," Rosenstein said. "I'm appropriately exercising my oversight responsibilities, and so I can assure you that the special counsel is conducting himself consistently with our understanding about the scope of his investigation."

But Rosenstein said the specific areas of Mueller's probe have not been made public, and said he has a "responsibility" not to outline the scope in public. He also said that because the public order didn't get into details, he and Mueller have had to clarify his precise mission in private.

"The specific matters are not identified in the order, so I discussed that with Director Mueller when he started, and we've had ongoing discussions about exactly what is in the scope of his investigation," he said. "To the extent there was any ambiguity about it, he's received my permission to include those matters within his investigation."

Smith took that as a sign the probe has been expanded, but Rosenstein said it's more of a clarification, although he seemed to hint it may have also included decisions to expand it.

"You're characterizing it as an expansion," Rosenstein said. "As I said, it's a clarification in most cases. But he understands that this is a special counsel, it's not an independent counsel."

Republicans have accused Mueller of exploring issues beyond Russia, and asked if Mueller is examining the finances of people on Trump's campaign. But Rosenstein again refused to answer specifically.