US legislation to disapprove of the nuclear agreement between world powers and Iran was introduced on Tuesday as President Barack Obama and Israeli PM Benjamin Netanyahu began lobbying support for their opposing positions.

Under the Iran Nuclear Review Act, which President Barack Obama signed into law in May, the Republican-led Congress has until September 17 to approve or disapprove of the nuclear deal between Iran and world powers announced on July 14.

The announced legislation means lawmakers will try to pass a disapproval resolution, which could cripple the agreement.

The top Republican in the US Senate, Mitch McConnell, said the Senate is also likely to consider a resolution of disapproval of the nuclear deal.

But Obama's diplomatic initiative won important support in Congress among his fellow Democrats.

Among them Bill Nelson, who some observers had considered a potential swing vote, said he would back the deal.

"As dangerous a threat as Iran is to Israel and our allies, it would pale in the threat posed to them and to us by a nuclear-armed Iran," Nelson said in a Senate speech announcing his decision.

‘Path to the bomb’

Israeli Prime Minister Benjamin Netanyahu strongly opposes the nuclear agreement, calling it a threat to the survival of the Jewish state.

Netanyahu made his case in a live webcast with more than 10,000 participants, according to the US Jewish groups that organised the event.

"The nuclear deal with Iran doesn't block Iran's path to the bomb," he said. "It actually paves Iran's path to the bomb."

Obama was to hold a private meeting at the White House later Tuesday with Jewish leaders - some who support the deal, some who oppose it, and others whose organisations are undecided.

The direct appeals from Obama and Netanyahu come amid an intense lobbying campaign on Capitol Hill, where lawmakers plan to vote on the nuclear deal next month. The vote will be one of Congress' most significant national security decisions in recent years.

As only one chamber of Congress is needed to sustain a veto, the White House is focusing its lobbying efforts on getting enough Democrats to sustain a veto.

Obama spokesman Josh Earnest said Monday that the White House is confident it can sustain a veto "at least in the House".

Obama planned to give a speech Wednesday outlining what he sees as the strengths of the nuclear deal.

(FRANCE 24 with REUTERS, AP)