Israel's Prime Minister Benjamin Netanyahu attends the weekly cabinet meeting in Jerusalem, in this March 3, 2013 file photo. [Photo/Agencies]

WASHINGTON - US Vice-President Joe Biden insisted on Monday that President Barack Obama was not bluffing about using force to thwart Iran's nuclear ambitions if all else fails, even as Israeli Prime Minister Benjamin Netanyahu called for a "credible military threat" against Tehran.

Seeking to reassure Israel and its US supporters just weeks before Obama visits the Jewish state, Biden cautioned that all options, including sanctions and diplomacy, must be exhausted to ensure that the international community will be supportive if military action is deemed necessary.

But Netanyahu, speaking moments later via satellite from Jerusalem, used his address to America's largest pro-Israel lobby to underscore Israeli impatience with US strategy on Iran, a message that could foreshadow his talks with Obama.

"Words alone will not stop Iran. Sanctions alone will not stop Iran. Sanctions must be coupled with a clear and credible military threat if diplomacy and sanctions fail," Netanyahu said to loud cheers at the American Israel Public Affairs Committee (AIPAC) policy conference in Washington.

Despite the tough rhetoric, the hawkish prime minister gave no indication that Israel was ready to act precipitously at a time when world powers have re-engaged with Iran in new negotiations and he himself is caught up in the delicate task of forging a new government after January's elections.

Netanyahu's remarks showed that the latest round of international talks with Iran in Kazakhstan last week had done little to soothe Israeli concerns. It is message he is likely to deliver face-to-face when he meets Obama, with whom he has had a notoriously testy relationship.

Despite that, Biden honed in on Obama's assertion in his 2012 AIPAC speech that he was ready to use force as a last resort to prevent Iran from getting a nuclear weapon. Tehran denies it is seeking one.

"President Barack Obama is not bluffing," Biden said to a standing ovation. "We are not looking for war. We are looking to and ready to negotiate peacefully, but all options, including military force, are on the table."

Netanyahu, who has hinted at Israeli plans to strike Iran's nuclear sites if it deems peaceful options to have failed, said Tehran was moving ever-closer to bomb capability and was using the negotiations to "buy time."

He has pressed the Obama administration to set strict limits on Tehran's nuclear development that would trigger a US military response, a demand that has fueled tensions between the two close allies. Obama has resisted setting such an ultimatum.

Biden urged caution to avoid losing international solidarity against Iran, which faces possibly the toughest sanctions ever assembled. "If, God forbid, the need to act occurs, it is critically important for the whole world to know we did everything in our power, we did everything that reasonably could have been expected to avoid any confrontation," Biden said.

He said there was still time for a diplomatic solution, though he warned "that window is closing".

After Biden's speech, AIPAC - which has not always seen eye-to-eye with the Obama administration - praised him for a "a very important statement today that the president is not bluffing".

Iran will top the agenda on Obama's first presidential visit to Israel, which Biden said would take place just before the Jewish holiday of Passover, beginning on March 25.