President Barack Obama “is not bluffing” when he says the U.S. will go to war if necessary to prevent Iran from getting a nuclear weapon, Vice President Joe Biden told the American Israel Public Affairs Committee in a speech on Monday.

“The president of the United States cannot, and does not, bluff,” Biden told the powerful pro-Israel lobbying group.

Republicans have charged that Obama’s threat to use force—cloaked in the traditional diplo-speak “all options are on the table”—lacks credibility. And they sharply question the president's commitment to Israel’s security.

Democrats hit back by pointing to public comments from senior Israeli officials including Defense Minister Ehud Barak praising the strength of American-Israeli bilateral cooperation.

Biden’s speech served to set up Obama’s trip to the Middle East later this month, including his first visit to Israel since taking office.

The vice president delivered a wide-ranging defense of the administration's policies towards the region and worked to convince any doubters in his audience that Obama is a friend to Israel—and sees U.S. security as inextricably bound up in that of the Jewish state.

"Even as circumstances have changed, one thing has not: our deep commitment to the security of the state of Israel," Biden declared. "That will not change as long as I and he are president and vice president of the United States. It's in our naked self-interest, beyond the moral imperative."

The vice president's remarks came one week after the Senate confirmed Republican former Sen. Chuck Hagel as defense secretary despite opposition from his fellow Republicans and inflammatory past comments about the influence of the "Jewish lobby" over American policy (for which Hagel apologized).

Biden didn't mention Hagel. But he did promise AIPAC that Secretary of State John Kerry would please them.

"He's a good man. You're going to be happy with Kerry," Biden said.

(Earlier Monday, during a stop in Saudi Arabia, Kerry echoed Biden's warnings to Iran. Kerry said a peaceful outcome was his "first choice," but underlined that "the window for a diplomatic solution simply cannot, by definition, remain open indefinitely.")

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Biden, at AIPAC, said the U.S. would stand firm in preventing Iran from obtaining a nuclear weapon.

"We have a shared strategic commitment. Let me make clear what that commitment is: It is to prevent Iran from acquiring a nuclear weapon. Period. Period. End of discussion. Period. To prevent, not contain, prevent," Biden said.

Israeli Prime Minister Benjamin Netanyahu, whose relationship with Obama is famously frosty, has warned against letting Iran get even the ability to build a nuclear weapon.

"If God forbid the need to act occurs, it is critically important for the whole world to know that we did everything in our power, we did everything that reasonably could have been expected to avoid any confrontation. That matters. Because God forbid if we have to act, it's important that the rest of the world is with us," Biden said.

The vice president also defended Obama's handling of the stalled Middle East peace process, which was eclipsed during his first term by the war in Afghanistan and other foreign policy crises.

"While there are those who question whether this goal will ever be reached, we make no apologies for continuing to pursue that goal. To pursue a better future. And he'll make that clear when he goes to Israel later this month," Biden said.

"He and I have spoken at length about this trip. I can assure he's particularly looking forward to having a chance to hear directly from the people of Israel, beyond their political leaders. And particularly the younger generation of Israelis," the vice president said.

Chris Moody contributed to this report.