Obama says Libyan 'mess' was his worst error
President Obama has said that failing to prepare for the aftermath of the ousting of Libyan leader Col Muammar Gaddafi was the worst mistake of his presidency.
Mr Obama was answering a series of questions on the highs and lows of his time in office on Fox News.
He said, however, that intervening in Libya had been "the right thing to do".
The US and other countries carried out strikes designed to protect civilians during the 2011 uprising.
But after the former Libyan leader was killed, Libya plunged into chaos, with militias taking over and two rival parliaments and governments forming.
Isil gained a foothold and Libya became a major departure point for migrants trying to reach Europe.
A UN-backed national unity government arrived in the capital Tripoli earlier this month but is still waiting to take charge.
The leader of the faction ruling western Libya has threatened to prosecute any of his ministers who co-operate with the UN-backed administration, contradicting an earlier announcement that the ministers would stand down.
President Obama told interviewer Chris Wallace his biggest regret was "probably failing to plan for the day after, what I think was the right thing to do, intervening in Libya."
It is not the first time President Obama has expressed regret over Libya. He told the 'Atlantic' magazine last month the operation had gone as well as he had hoped, but that Libya was now "a mess".
In that interview, he also criticised France and the UK, in particular saying that the British Prime Minister David Cameron had become "distracted" after the intervention.
It was a rare rebuke for a close ally and one which BBC correspondents at the time said angered Downing Street.
Rival militias have been fighting for control in Libya.
President Obama told Fox that his biggest accomplishment in office was "saving the economy from the great depression".
He said the best day of his presidency was when he passed the healthcare reforms. The worst was responding to the mass shooting at Sandy Hook elementary school.
Mr Obama discussed his legacy in a BBC interview last year, saying that his failure to pass tighter gun control laws was the biggest frustration of his presidency.