Vice President Joe Biden, projected on screens, gestures as he addresses the American-Israeli Public Affairs Committee (AIPAC) 2013 Policy Conference, Monday, March 4, 2013, at the Walter E. Washington Convention Center in Washington. (Susan Walsh/AP)

Vice President Biden sought Monday to play down years of tension between the Obama administration and the Israeli government over how best to pursue peace with the Palestinians, focusing his remarks to a powerful Israel-advocacy group on preventing Iran from developing nuclear weapons.

Speaking to the American Israel Public Affairs Committee — the largest and traditionally most hawkish pro-Israel lobbying organization — Biden reassured the audience, which included Israeli Defense Minister Ehud Barak, that Obama is “not bluffing” when he threatens military action to keep Iran from achieving nuclear-weapons capability.

As Obama has done in previous appearances before the group, Biden said the administration prefers a diplomatic solution to control Iran’s uranium-enrichment program. The Islamic Republic says the program is being developed for peaceful means, despite mounting evidence to the contrary.

But in stating Obama’s pledge to Israel, Biden said, “Let me make clear what that commitment is: It is to prevent Iran from acquiring a nuclear weapon. Period. End of discussion. Prevent — not contain — prevent.”

“Big nations can’t bluff,” Biden continued. “And presidents of the United States cannot and do not bluff. And President Barack Obama is not bluffing.”

In the heat of the U.S. presidential election last year, when his commitment to Israel emerged as an issue, Obama stated the same position to AIPAC. But he also warned that “now is not the time for bluster.”

On Monday, Biden again cautioned against a rush to war, especially as a series of popular uprisings known collectively as the Arab Spring continue to remake the Middle East. He said that the “window is closing” for diplomacy to work” but that there is still time and space to achieve the outcome.

Obama is scheduled to visit Israel and the Palestinian territories for the first time as president later this month, although the trip could be postponed if a new Israeli government is not yet in place after January elections.

Obama and Prime Minister Benjamin Netanyahu, who addressed the gathering via satellite after Biden spoke, have had an uneasy relationship over the past four years, primarily over the Palestinian issue.

At the same time, Obama has increased U.S. military aid to and collaboration on anti-missile systems with Israel. The two leaders also generally agree on the approach to Iran, although they have differed publicly over a possible timeline for military action against its nuclear sites.

Their relationship took shape amid tensions over Obama’s early approach to reviving Middle East peace talks soon after he took office.

Palestinian leaders did not join the U.S.-brokered peace negotiations until the final month of Netanyahu’s building moratorium, and those collapsed quickly afterward when the Israeli prime minister declined to renew the freeze.

Biden on Monday sought to turn the page on those differences, speaking mostly about Obama’s record in defense of Israel.

“It’s going to require hard steps on both sides,” he said. “But it’s in all of our interests — Israel’s interest, the United States’ interest, the interest of the Palestinian people. We all have a profound interest in peace. To use an expression of a former president, Bill Clinton: We’ve got to get caught trying.”

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