US:Senator Hillary Clinton has drawn another distinction between herself and Senator Barack Obama by refusing to rule out the use of nuclear weapons against Osama bin Laden or other terrorists in their hiding places in Afghanistan and Pakistan.
Ms Clinton's comments on Thursday came in response to Mr Obama's remarks earlier in the day that nuclear weapons are "not on the table" in dealing with ungoverned territories in the two countries, and continued a steady tug-of-war among the Democratic candidates for president over foreign policy.
"I think it would be a profound mistake for us to use nuclear weapons in any circumstance" in Afghanistan or Pakistan, Mr Obama said. He then added that he would not use such weapons in situations "involving civilians. Let me scratch that," he said. "There's been no discussion of nuclear weapons. That's not on the table."
The Illinois senator was responding to a question about whether there was any circumstance in which he would be prepared or willing to use nuclear weapons in Afghanistan and Pakistan to defeat terrorism and bin Laden.
"There's been no discussion of using nuclear weapons and that's not a hypothetical that I'm going to discuss," Mr Obama said.
When asked whether his answer also applied to the possible use of tactical nuclear weapons, he said it did.
By the afternoon, Ms Clinton had responded with an implicit rebuke of her Democratic rival.
"Presidents should be careful at all times in discussing the use and non-use of nuclear weapons," she said, adding that she would not answer hypothetical questions about the use of nuclear force.
"Presidents since the cold war have used nuclear deterrents to keep the peace, and I don't believe any president should make blanket statements with the regard to use or non-use."
At a debate last week in South Carolina, Ms Clinton directly criticised Mr Obama for saying he would meet with leaders traditionally hostile to the US.
He responded, and the sniping went on most of the week. But when Mr Obama said in a speech on terrorism on Wednesday that he would use military force to go after terrorists in Pakistan, even without President Pervez Musharraf's permission, Ms Clinton did not join in the criticism of him by other Democrats.
In a letter to supporters entitled "The war we need to win", Mr Obama has also called for the country to "stop fighting the wrong war" in Iraq and to focus on the al-Qaeda threat that became a lower priority after the Iraq war began. "We are overdue for a major change of course in our foreign policy," the letter read.
US officials rarely rule out nuclear attacks as a matter of diplomacy, preferring to keep the threat as a deterrent.
Yet several foreign policy experts said Mr Obama was essentially right: It would be unwise to target an individual or small group with nuclear weapons that could leave massive collateral damage, killing civilians and worsening the United States's image around the world.
Michael O'Hanlon, a Brookings Institution scholar who recently wrote that the war in Iraq is getting better, said Mr Obama "clearly gave the right answer".
"He's certainly right to say you would never use a nuclear weapon to get Osama bin Laden," Mr O'Hanlon said. If intelligence officials were able to locate bin Laden with the precision required for a nuclear attack, he said, they would also be able to catch or kill him by more conventional means that would not then signal to the rest of the world that using nuclear force is acceptable.