President Bush's former envoy to the United Nations says using military force against Iran would be preferable to allowing the country to acquire nuclear weapons.

John Bolton gained a reputation for speaking out during his 17 months as U.S. ambassador to the world body. But his remarks Tuesday night were some of his boldest yet, especially concerning Tehran.

"I believe that ultimately the only real prospect of getting Iran to give up nuclear weapons is to change the regime," Bolton told reporters after an off-the-record speech to the Hudson Institute, a nonpartisan policy research organization.

How should this be done?

"By the force of the Iranian people themselves," Bolton replied. "But if the alternative is a nuclear Iran, as unpleasant as the use of military force would be, I think the prospect of a nuclear Iran is worse."

The U.N. Security Council is considering new sanctions against Tehran for refusing to suspend uranium enrichment, a process that can produce fissile material for nuclear weapons as well as fuel for nuclear power plants. Tehran's reaction to U.N. sanctions imposed in December was to step up its enrichment of uranium.

"I think Iran's record is clear that they're never going to give up the pursuit of uranium enrichment," Bolton said, "and I think that there's no disagreement within their leadership that that's the road to nuclear weapons."

Bolton arrived at the United Nations in August 2005, a controversial figure appointed by Bush during a Congressional recess because he twice failed to be confirmed by the Senate. Still unable to get Senate backing, he stepped down in December.

Now back at the conservative American Enterprise Institute, he says he's writing a book about his days at the U.N. titled "Surrender is Not an Option." Published by Simon & Schuster, it is due out in November.

Bolton also criticized the U.S. government for releasing $25 million in frozen North Korean assets held by a Macau bank suspected of helping North Korea launder money from counterfeiting and other illegal activities.

The United States had promised to release the funds as part of international efforts to roll back the communist regime's nuclear weapons program.

"I think it's a signal of weakness," he said. "It's a terrible signal to Iran and other would-be proliferators."

The former ambassador also said it was time to contemplate regime change in Sudan, whose government is accused of inciting a conflict in the country's Darfur region that has killed 200,000 people and displaced 2.5 million since 2003.

He said so many elements of Sudan are dissatisfied with the government that there would be a "lot of candidates" for undertaking regime change.