"I'm the one who presented it to the world, and (it) will always be a part of my record. It was painful. It is painful now," Powell said in an interview with Barbara Walters on ABC News.
The presentation by the soldier-diplomat to the world body in February 2003 lent considerable credibility to President Bush's case against Iraq and for going to war to remove President Saddam Hussein.
In the speech, Powell said he had relied on information he received at Central Intelligence Agency briefings. He said Thursday that then-director George Tenet "believed what he was giving to me was accurate."
But, Powell said, "the intelligence system did not work well."
"There were some people in the intelligence community who knew at the time that some of those sources were not good, and shouldn't be relied upon, and they didn't speak up," Powell said.
"That devastated me," he said.
Powell in the TV interview also disputed the Bush administration's linking of Saddam's regime with terrorists.
He said he had never seen a connection between Baghdad and the 9-11 attacks on New York and Washington in 2001. "I can't think otherwise, because I'd never seen evidence to suggest there was one," he said.
Still, Powell said that while he has always been a "reluctant warrior" he supported Bush on going to war the month after his U.N. speech. "When the president decided that it was not tolerable for this regime to remain in violation of all those U.N. resolutions I am right there with him with the use of force," Powell said.