US President Barack Obama criticized "loose talk of war" on Sunday as he pleaded for patience in ending the nuclear standoff with Iran, arguing that sustained international pressure can work.

On the eve of White House talks with Israeli Prime Minister Benjamin Netanyahu, Obama sought to reassure a powerful pro-Israel lobby by vowing to use force if necessary and stressing Israel's own right to defend itself.

"We will do what it takes to preserve Israel's qualitative military edge -- because Israel must always have the ability to defend itself, by itself, against any threat," Obama said.

While Obama's remarks on Israel's self-defense drew a special warm welcome from Netanyahu, who was visiting Canada, the US president also stressed diplomacy at a time when Israeli patience with Iran may be running low.

Speaking to the American Israel Public Affairs Committee (AIPAC) in Washington alongside Israeli President Shimon Peres, he said sanctions were working and cautioned against the saber-rattling of recent months.

"Because of our efforts, Iran is under greater pressure than ever before," he told thousands of delegates at the AIPAC annual policy forum.

"I firmly believe that an opportunity remains for diplomacy -- backed by pressure -- to succeed," Obama said.

"Already, there is too much loose talk of war," he said, adding that such talk only helps Iran and its nuclear program by "driving up" oil prices.

"For the sake of Israel's security, America's security, and the peace and security of the world, now is not the time for bluster," he said.

"Now is the time to let our increased pressure sink in, and to sustain the broad international coalition that we have built."

US intelligence is said to believe Iran does not currently intend to produce nuclear weapons, though it may be seeking the capacity to do so, and Washington has emphasized the importance of deterrent sanctions and diplomacy.

But Israel is reportedly eager to move more quickly and decisively against Iran's nuclear activities, using a military strike to prevent it from obtaining even the capacity to take a decision to produce nuclear weapons.

AIPAC distributed a leaflet saying: "Iranian nuclear weapons capability: Unacceptable."

Obama stopped short of vowing to prevent such a break-out capability, but did say: "Iran's leaders should know that I do not have a policy of containment; I have a policy to prevent Iran from obtaining a nuclear weapon.

"And as I've made clear time and again during the course of my presidency, I will not hesitate to use force when it is necessary to defend the United States and its interests."

But experts warn that Israel fears that the US and Israeli clocks for military action may not be synchronized and that Washington might seek to delay strikes until it is too late.

Iran insists its nuclear program is solely for civilian energy purposes and medical research.

Netanyahu, who clashed with Obama last year over the Middle East peace talks, told journalists in Ottawa that he welcomed the US president's refusal to rule out military action to prevent Iran from obtaining a nuclear weapon.

He also said he appreciated the fact that Obama's comment on containment.

"Equally and in my judgment perhaps most important of all, I appreciate the fact that he said Israel must be able to defend itself, by itself, against any threat," Netanyahu said.

Josh Block, a former spokesman for AIPAC who is now a senior fellow at the Progressive Policy Institute, echoed Netanyahu's praise.

"The president said some welcome things today on Iran, including making clear that he has a policy of prevention not containment, explicitly pointing to a military option, delivering an extended explanation of why it is in America's interest to stop Iran, and in particular making explicitly clear that Israel has a sovereign right to defend themselves as they see fit," Block said.

Speaking before Obama, Peres said Israel "shall prevail" if forced to fight Iran, which he called "an evil, cruel and morally corrupt regime" bent on controlling the Middle East.

"Iran is the center, the sponsor, the financer of world terror. Iran is a danger to the entire world," he said.

Stressing unity, Peres said "the United States and Israel share the same goal -- to prevent Iran from developing a nuclear weapon. There is no space between us."