Obama victory as Democrats defeat legislation against Iran nuclear deal

US President Barack Obama hailed a Congressional vote allowing a nuclear deal with Iran to go ahead on Thursday, saying work would now shift to implementing and verifying the accord.

"This vote is a victory for diplomacy, for American national security, and for the safety and security of the world," Obama said in a written statement.

After hours of debate in the Senate on Thursday, a vote on a Republican-led effort to block the Iran deal fell two votes short of the 60 needed to advance a resolution disapproving putting the accord to a final vote.

After a bitter and lengthy campaign to wrangle votes, winning over the support of 42 Senators saved Obama the embarrassment of having to veto a resolution of disapproval and means the legislation aimed at sabotaging the deal is essentially dead.

"I am heartened that so many Senators judged this deal on the merits, and am gratified by the strong support of lawmakers and citizens alike," said Obama.

"We will turn to the critical work of implementing and verifying this deal so that Iran cannot pursue a nuclear weapon."

It is rare for a US president to fail to secure Congress's backing for a major foreign policy initiative. But Thursday's vote is being seen as a victory for the White House nonetheless.

Iranian Americans laud deal

The National Iranian American Council (NIAC) applauded the vote in a statement on Thursday.

"This is a stunning victory for supporters of peace and diplomacy," NIAC executive director Jamal Abdi said in the statement. "This vote should settle the debate once and for all that this is a good deal."

"Instead of revisiting this vote or re-litigating the terms of the deal, it is now time to focus on implementing the agreement and doubling down on diplomacy rather than militarism."

NIAC president Trita Parsi said in a separate statement that he hoped that the deal could lead to better relations between Iran and the US.

"The nuclear deal only resolves one out of many areas of US-Iran tensions – it does not guarantee that Iran and the US will completely bury the hatchet," he said.

"But just because Iran and the US won’t become best friends tomorrow doesn’t mean they are destined to be worst enemies forever."

He added: "Focus must now turn to how the newly won dialogue with Iran can be used to stabilise the Middle East, push back against radicalism and terrorism, and improve Iran’s deplorable human rights record."

The Iran agreement offers sanctions relief in exchange for curbs on Iran's nuclear programme.