Sen. Hillary Rodham Clinton confirmed Monday that as president she would be willing to use nuclear weapons against Iran if it were to launch a nuclear attack on Israel.

Clinton's remarks, made in an interview on MSNBC's "Countdown With Keith Olbermann," clarified a statement she made last week in a Democratic presidential debate in Philadelphia. In that debate, Clinton, D-N.Y., said an Iranian attack on Israel would bring "massive retaliation," without defining what the phrase meant.

In the interview Monday, Clinton affirmed that she would warn Iran's leaders that "their use of nuclear weapons against Israel would provoke a nuclear response from the United States."

She said U.S. allies in the Middle East were being "intimidated and bullied into submission by Iran," raising the prospect of an "incredibly destabilizing" arms race in the region.

"I can imagine that they would be rushing to obtain nuclear weapons themselves" if Iran were to develop a nuclear arsenal, she said.

Clinton said it was vital that the United States create a new "security umbrella" to reassure Israel and its other allies in the region that they would not be threatened by Iran. She said she would tell them that "if you were the subject of an unprovoked nuclear attack by Iran, the United States, and hopefully our NATO allies, would respond to that."

Clinton seeks tougher profile than Obama Clinton's hinting at a nuclear option last week set off a wave of commentary in political circles that she was seeking to position herself as a hawk as the primary campaign winds toward an end. Her opponent for the Democratic nomination, Sen. Barack Obama of Illinois, has said that he would not rule out any options if Iran were to become a nuclear power, but he has not explicitly said he would be willing use nuclear weapons.

Clinton's remarks reflected the theme of her latest advertising in Pennsylvania, where Democratic voters go to the polls Tuesday with analysts in both camps saying she must win the state's primary if she is to remain a credible candidate.