Asgar Oladi, the secretary-general of the Islamic Coalition Party, made the comments about 10 days after saying that he didn't believe the two opposition figures, who have been under house arrest since 2011, had "seditious" intentions.
He had also said that the clerical establishment should not easily give up on Musavi, a former prime minister, and Karrubi, a former parliament speaker.
"The sedition" is the term Iranian leaders have used to refer to the opposition Green Movement that emerged following the disputed 2009 reelection of Iranian President Mahmud Ahmadinejad.
In his interview with Mehr published on January 9, Asgar Oladi claimed that the United States, Britain, and Israel were the main leaders of the postelection unrest that pushed the Islamic republic into serious crisis.
He said Musavi and Karrubi, whom he credited with having served the Islamic establishment at some point, were caught in the so-called sedition. "I've said clearly that they stood against the establishment and the people, and they have to be held responsible," he said.
Before Asgar Oladi, another prominent hard-line politician, Mashhad Friday Prayer leader Ayatollah Ahmad Alamolhoda, had denied having said that Musavi and Karrubi should not be considered "seditionists."
"My belief is that America and Britain were behind the sedition, Musavi and Karrubi paved the way for the sedition, and they are themselves seditionists," he said.
Alamolhoda made the comments on December 30, two days after having been quoted by the Fars news agency as saying that unjust accusations shouldn't be made against Musavi and Karrubi.
The reason for the U-turn and the pivot back is not clear.
Both men had reportedly come under criticism for the apparent softening of their tone regarding the two opposition figures, who have accused Iranian leaders of election fraud and human rights abuses.
RFE/RL's Radio Farda reports that a senior commander of the powerful Islamic Revolutionary Guards Corps (IRGC) had also questioned the comments.
An IRGC cultural deputy, Mohammad Reza Moghadamfar, said that perhaps Asgar Oladi had misspoken when he defended Musavi and Karrubi. "Such comments are very unlikely from someone like Asgar Oladi. He probably meant something else," he said.
Moghadamfar compared the two opposition leaders to the leader of the opposition Mujahedin-e Khalq Organization, Massoud Rajavi, and said that he didn't consider theirs any less of a "betrayal" than Rajavi's.
The Mujahedin-e Khalq Organization is considered a terrorist organization by the Islamic republic. Members of the group fought alongside Saddam Hussein's forces in the 1980-88 Iran-Iraq War that left hundreds of thousands of dead on both sides.
-- Golnaz Esfandiari