Appearing on Libyan state television early on Monday morning, Seif al-Islam said his father is in the country and backed by the army. "We will fight to the last minute, until the last bullet."
He said his father was leading the fight, although he added that some military bases, tanks and weapons had been seized.
"We are not Tunisia and Egypt," the younger Gaddafi said, referring to the successful uprisings that toppled longtime regimes in Libya's neighbours
He acknowledged that the army made mistakes during protests because it was not trained to deal with demonstrators but added that the number of dead had been exaggerated, giving a death toll of 14 in Tripoli and 84 in Benghazi.
Human Rights Watch put the number at 174 through Saturday, and doctors in the eastern city of Benghazi said more than 200 have died since the protests began.
Marwan Bishara, Al Jazeera's senior analyst, termed Seif al-Islam's speech as "desperate".
"It sounded like a desperate speech by a desperate son of a dictator who's trying to use blackmail on the Libyan people by threatening that he could turn the country into a bloodbath.