Clinton said the "evidence is not sufficient" to confirm that a son was killed, according to excerpts of an interview the chief US diplomat gave to ABC World News.
"But we've heard that, we've heard about other people close to him reaching out to people that they know around the world," she said.
Clinton added that if indeed a Gaddafi son had been killed, it would not have been by US forces.
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"We hear many different things, but we know it's not us," she said, according to ABC.
Tuesday was the fourth day of coalition air strikes involving US, British and French forces. Clinton did not identify the source of the reporting she had heard, nor identify the son.
Unconfirmed media reports identified the son as 27-year-old Khamis Gaddafi, and that he was killed after a kamikaze Libyan pilot crashed into alternatively the regime's main Tripoli headquarters or military barracks where he was staying.
British tabloid The Sun reported Khamis Gaddafi suffered burns in the strike and later died in hospital, and quoted the website of Libyan Youth Movement as naming the Libyan pilot as Muhammad Mukhtar Osman, and praising him as a martyr.
