A powerful US pro-Israel lobby on Sunday opens an annual conference where thousands of delegates seem intent on hearing President Barack Obama echo the Jewish state's fears about Iran's nuclear aims.

Obama's speech to the American Israel Public Affairs Committee may well set the tone for his meeting Monday with Israeli Prime Minister Benjamin Netanyahu, who will also speak to AIPAC after the pair's White House encounter.

The events come as questions grow over whether Israel is preparing to launch a pre-emptive strike against Iran and whether Washington will urge Israel to delay military action in order to allow time for crippling sanctions to work.

AIPAC, which touts itself as the most influential US foreign policy lobby, will also host Israeli President Shimon Peres, who will give a speech and meet with Obama here on the opening day of the annual policy conference.

In all, a record 13,000 people are to due attend this year: students, legislators, government and military officials, foreign ambassadors, analysts, and rabbis and other religious figures from across the United States and Israel.

Iran is expected to be the dominant theme at AIPAC, unlike last year when Obama tried to rally support behind US-brokered Palestinian-Israeli peace talks that have have since foundered.

"This year's conference gathers at a time when the global threat posed by Iran is at an all-time high," AIPAC said in a statement, adding that both Obama and Nethanyahu would tackle the threat in their speeches.

"Iran is nearing nuclear-weapons capability, jeopardizing American national security and threatening our friends in the Gulf as well as our broader interests in the Middle East," it said.

It warned of heightened Iranian terrorist activity and said "Iran's leaders call for Israel to be wiped off the map as they pursue nuclear weapons that would pose an intolerable threat to the Jewish state."

Iran denies US and Israeli charges of a weapons drive, saying its nuclear program is solely for peaceful purposes.

AIPAC's annual policy conference "is a subset of the broader strategy and the tone of the meeting" between Obama and Netanyahu on Monday, according to Aaron David Miller, a former US Middle East peace negotiator.

"AIPAC is a way to orchestrate what I think will be probably one of the best meetings the prime minister and the president have ever had, in large part because neither of them want a fight," he told AFP.

During his visit to Washington last year, Netanyahu engaged Obama in a public spat over the Israeli-Palestinian peace process.

Obama will likely say "Iran's efforts to acquire a nuclear (weapons) capacity, or certainly to weaponize... must be stopped," said Miller who is now at the Woodrow Wilson International Center for Scholars.

He said he will also make clear the United States "intends to continue to ratchet up the pressure" after imposing fresh sanctions in the last few months that target Iran's oil industry.

As for whether Washington is prepared to launch military action against Iran, Miller said Obama "will be elusive about it, for sure, but he will make it unmistakably clear that it's still very much an option."

The two leaders will finesse their differences in their meeting, he said.

"Bibi (Netanyahu) would love a green light from Obama on the issue of attacking Iran, if he feels the need to. And Obama wants a red light from Bibi that he won't (attack)," Miller said.

"Neither side will get that from one another, but they will manage the problem because they must," he said.

"They must emerge from this meeting with unmistakable clarity and commonality of interests for the constituencies that need to hear it: the Russians, the Chinese and the Europeans, the Iranians for sure," he said.

Obama, Miller said, will also try to avoid "giving the Republicans an issue to hammer him with" while "keeping the pro-Israeli community reassured" as he faces re-election this year.

David Makovksy, with the Washington Institute for Near East Policy, said Obama is likely to try to reassure Israel's supporters about US intentions on Iran.

"The fact that he's agreed to meet (AIPAC) suggests that he wants them to clearly understand that he has no illusions about the Iranian nuclear program and when he says all options are on the table, he means it," Makovsky told AFP.

"I think the tone he sets there will be very significant," he said.