SDEROT, Israel — Democratic presidential candidate Barack Obama defended his proposal to negotiate with Iran Wednesday and said he would use "big sticks and big carrots" to persuade the country's leaders not to develop nuclear weapons.

"My whole goal in terms of having tough, serious direct diplomacy is not because I'm naive about the nature of any of these regimes. I'm not," Obama said at a press conference. "It is because if we show ourselves willing to talk and to offer carrots and sticks in order to deal with these pressing problems, and if Iran then rejects any overtures of that sort, it puts us in a stronger position to mobilize the international community to ratchet up the pressure on Iran."

He said a nuclear-armed Iran would pose a threat to both Israel and the United States.

The campaign of Republican presidential candidate John McCain quickly responded that Obama was backtracking on his expressed willingness to meet with Iran's leaders without preconditions.

A year ago, Obama was asked whether he would meet personally, without preconditions, with leaders of Iran and other hostile nations during the first year of his administration to resolve differences with the United States. Obama said he would.

On Wednesday Obama said, "I think that what I said in response was that I would at my time and choosing be willing to meet with any leader if I thought it would promote the national security interests of the United States of America. And that continues to be my position. That if I think that I can get a deal that is going to advance our cause, then I would consider that opportunity. But what I also said was that there is a difference between meeting without preconditions and meeting without preparation."

This was Obama's second press conference during his trip to Afghanistan, Iraq, the Middle East and Europe, part of his campaign's attempt to establish his credentials as a potential world leader. He spoke in Sderot, near the Gaza border. The city has been a frequent target of rocket attacks from Palestinian militants, and the news conference was held beside a display of the spent rockets.

Obama tried to use Wednesday's event to allay doubts about his support for Israel. Many Israelis are worried by Obama's willingness to talk to Tehran, a bitter enemy of the Jewish state. Many U.S. Jewish voters supported Obama's rival Hillary Rodham Clinton for the Democratic presidential nomination, and some have questioned his commitment to Israel.