John Kerry ignited a debate Wednesday over former president Bush's policy toward Iran when he said at a Senate hearing that the Obama administration has abandoned calls for "regime change" in Tehran and expects a response to its diplomatic outreach.

"That is not the current policy of this new administration, and it is important for Iran to understand that," Kerry said during a hearing of the Senate Foreign Relations Committee. "Just as we abandon calls for regime change in Tehran and recognize the legitimate Iranian role in the region, Iran's leaders need to moderate their behavior."

But the Bush administration mostly stopped calling for regime change in Iran during its second term, said Nicholas Burns, a former undersecretary of state under Bush. Burns told Bloomberg after the hearing that the Bush administration stressed negotiations starting in 2006.

"That was the focus," said Burns, who now teaches at Harvard University's John F. Kennedy School of Government. "The Iranians walked away from that."

Asked to respond to Burns' comments after the hearing, Kerry spokesman Frederick Jones told FOXNews.com that "Sen. Kerry stands by that statement. Everyone know that regime change was the implicit policy of the Bush administration for many years."

Burns, in his testimony at the hearing, urged Obama to publicly repudiate regime change.

"I think it would be helpful if the American administration was to say overtly and clearly, 'that's not our policy,'" Burns said.

But he warned that Iran should expect harsher sanctions if it goes on with its uranium enrichment activities.

Bush stirred speculation that the U.S. was considering imposing a regime change by famously calling Iran a member of the "axis of evil" and declaring its mission to assist in democratization abroad.

"Iran remains the world's primary state sponsor of terror -- pursuing nuclear weapons while depriving its people of the freedom they seek and deserve," Bush said at his State of the Union address in 2005. "And to the Iranian people, I say tonight: As you stand for your own liberty, America stands with you."

But Bush officials at the time denied any plans to help depose the Muslim clerics who run the country.