By Susan Cornwell

WASHINGTON (Reuters) -- A probe of the 2012 Benghazi attacks may have violated congressional ethics rules, House of Representatives Democratic leader Nancy Pelosi said on Thursday after a top Republican indicated it was aimed at hurting Democrat Hillary Clinton's presidential candidacy.

Angry Democrats called for the Benghazi panel to be disbanded following the remarks on Tuesday evening by House Majority Leader Kevin McCarthy. He is campaigning to be the next speaker of the House when the current speaker, John Boehner, retires on Oct. 30.

McCarthy on Thursday voiced regret for making the remarks after some House Republicans said they thought he should apologize for, or explain, them. Others expressed understanding for what they saw as a media stumble.

"Everybody thought Hillary Clinton was unbeatable, right?" McCarthy told Fox News on Tuesday. "But we put together a Benghazi special committee, a select committee. What are her (poll) numbers today? Her numbers are dropping."

Democrats said McCarthy's comments revealed the truth about the committee and countered the long-standing Republican contention that the panel was set up to find out what happened in the 2012 attacks on U.S. facilities in Benghazi, Libya, that killed four Americans.

Pelosi said political efforts by the Benghazi committee could violate ethics laws that ban using taxpayers' dollars for political purposes.

"The question is, is this an ethics violation of the rules of the House?" she said. "I think he (McCarthy) clearly, gleefully claimed that this had a political purpose and had a political success."

McCarthy told Fox News on Thursday he "did not intend to imply in any way" that the committee's work was political.

Asked if he had apologized to the panel's chairman, Representative Trey Gowdy, McCarthy said: "I talked to Trey and I told him I regret that this has ever taken place ... and Trey goes: 'I know it's not your intention.'"

Boehner, a Republican, said the committee would continue its work. "This investigation has never been about former Secretary of State Clinton and never will be," he said in a statement that did not mention McCarthy.

McCarthy's words were widely considered a major gaffe. They were some of his first public remarks after jumping into the race to replace Boehner as speaker. He is the leading candidate for the post.

Asked if his comments could hurt his chances, McCarthy told Fox News: "This is not what you're going to see as speaker of the House."

(Reporting by Susan Cornwell and Richard Cowan; Editing by Christian Plumb and Jonathan Oatis)