"I think it would be a profound mistake for us to use nuclear weapons in any circumstance," Obama said, with a pause, "involving civilians." Then he quickly added, "Let me scratch that. There's been no discussion of nuclear weapons. That's not on the table."
Obama was responding to a question by the Associated Press about whether there was any circumstance where he would be prepared or willing to use nuclear weapons in Afghanistan and Pakistan to defeat terrorism and al-Qaida leader Osama bin Laden.
"There's been no discussion of using nuclear weapons and that's not a hypothetical that I'm going to discuss," Obama said after a Capitol Hill breakfast with constituents.
When asked whether his answer also applied to the possible use of tactical nuclear weapons, he said it did.
The Illinois senator warned Pakistani President Gen. Pervez Musharraf in a major foreign policy speech Wednesday that he would use U.S. military force in Pakistan even without Musharraf's permission if necessary to root out terrorists.
Asked about Obama's speech and his comments about nuclear weapons, Clinton chided her fellow senator about addressing hypotheticals.
"Presidents should be very careful at all times in discussing the use or non-use of nuclear weapons. ... I don't believe that any president should make any blanket statements with respect to the use or non-use of nuclear weapons," Clinton said.
Asked about the notion of unilateral U.S. military action in Pakistan to get al-Qaida leadershipo she said: "How we do it should not be telegraphed or discussed for obvious reasons."
Another Democratic rival, Sen. Joe Biden, also criticized Obama's comments about unilateral military action in Pakistan to pursue terrorists.
"It's a well-intended notion he has, but it's a very naпve way of figuring out how you're going to conduct foreign policy," the chairman of the Senate Foreign Relations Comittee said on a radio show.
Sen. Chris Dodd, a member of the Foreign Relations Committee along with Obama, also took his rival to task.
"Over the past several days, Senator Obama's assertions about foreign and military affairs have been, frankly, confusing and confused. He has made threats he should not make and made unwise categorical statements about military options," Dodd said in a statement.
Pakistan has nuclear weapons and is politically unstable, raising concerns that the current military leadership could be replaced by religious fanatics who would be less cautious in using the weapons.
Obama warned that terrorists in the mountains of Pakistan are planning another attack on the United States, after already killing 3,000 Americans in their 2001 attacks.
"It was a terrible mistake to fail to act when we had a chance to take out an al-Qaida leadership meeting in 2005." he said. "If we have actionable intelligence about high-value terrorist targets and President Musharraf will not act, we will."
An explosion of household gas occurred in a nine-storeyed apartment building in the city of Shakhty, the Rostov region of Russia. The blast destroyed two storeys of the building