Libyan leader Muammar Gaddafi agreed to hold internationally-supervised elections, his son said, which was dismissed by rebels Thursday.

"They could be held within three months. At the maximum by the end of the year, and the guarantee of transparency could be the presence of international observers," Gaddafi's son Saif al-Islam told Italian daily Corriere della Sera in an interview published on Thursday.

He said the elections could be supervised by bodies including the European Union, the African Union, the United Nations or even NATO, which has intensified air strikes against Gaddafi's forces.

"Gaddafi's government has lost legitimacy, so he is not supposed to ask for elections and we will not negotiate with him," Jalal Gallal, the rebels' spokesman, told Xinhua by phone.

"The international community has been calling on Gaddafi to pull back his troops and allow humanitarian aid to reach the Libyan people," he said, adding that "the only choice for Gaddafi is to step down."

The United States said Thursday that it is "a little late" for Gaddafi to broach any proposal as his days are numbered.

"It's a little late for any proposal by Gaddafi and his circle for democratic change. It's time for him to go," the U.S. State Department spokeswoman Victoria Nuland told reporters.

She said the pressure the international community has brought on Gaddafi and his regime is "having an effect," with over 50 senior-level diplomatic and government officials having defected.

"So the guy is getting increasingly lonely, increasingly isolated. His days are numbered," she added.