Saif al-Islam Gaddafi's arrest had been reported by the rebels but he appeared before foreign media in Tripoli early on Tuesday, raising questions as to the rebels' credibility.
"There was no official confirmation from the National Transitional Council," ICC official Fadi el-Abdallah said. "Different answers were given. That was a little ambiguous."
He added that statements from both the ICC and the prosecutor on Monday said they had received information about the arrest but that they were trying to confirm this.
The office of the prosecutor, which told Reuters early on Monday it had confirmation from sources that Saif had been arrested, has not yet responded to requests for comment.
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