"This was a direct operation to assassinate the leader of this country. This is not permitted by international law. It is not permitted by any moral code or principle.
"What we have now is the law of the jungle,
" Ibrahim told a news conference.
"We think now it is clear to everyone that what is happening in Libya has nothing to do with the protection of civilians."
"It seems there was intelligence that was leaked. They knew about something. They expected him for some reason. But the target was very clear, very, very clear. And the neighbourhood, yes of course, because the leader family has a place there, you could expect of course it would be guarded, but it is a normal neighbourhood. Normal Libyans live there," he said.
The 29-year-old Saif al-Arab Gaddafi is the most unknown of the Libyan leader's children, Al Jazeera's Anita McNaught, reporting from Tunisia, said.
"He's one of the low-profile of his children and has been largely invisible since the conflict began", she said.
"He hasn't been visible in any significant form. He hasn't appeared on TV or made any speeches, he hasn't been on any crowd-rallying marches."
Ibrahim said al-Arab was a civilian and a student who had studied in Germany.
Ibrahim had earlier taken journalists to the remnants of a house in Tripoli, which Libyan officials said had been hit by at least three missiles. Given the level of destruction, it is unclear that anyone could have survived.
Three loud explosions were heard in Tripoli on Saturday evening as jets flew overhead. Volleys of anti-aircraft fire rang out following the first two strikes, which were followed by a third.