Prominent Republican Senators indicated on 22 July that they hope to defeat the passage of a landmark nuclear deal with Iran when it comes up for a vote.

US President Barack Obama, a Democrat, and other top officials have begun a full-bore effort to persuade sceptical lawmakers not to fight the deal, and today Secretary of State John Kerry met with Members of Congress to brief them on the agreement.

But as he emerged from the meeting, Republican Senator and presidential candidate Lindsey Graham was scathing in his criticism of the deal with Iran.

"So the construct that Secretary Kerry has in his mind, that there is a moderate hard-line element and we need to empower the moderates, I think is a gross misunderstanding of Iran. And the idea that you have to take this deal or we'll have a war comes from a weak-minded president and a Secretary of State who wants a deal way too badly.

"At the end of the day there is a better deal awaiting the world and the United States with a new president. This is the best deal Barack Obama could get because he is so weak in the eyes of our enemies and so unreliable in the eyes of our friends. So I hope a 'no' vote will be seen as empowering the next president," he said.

Obama has promised to exercise his veto if Congress rejects the deal, and overriding it would require a two-thirds majority of both the House of Representatives and Senate.

Republican Senator Tom Cotton said today he did not believe the administration had the numbers to overcome a "no" vote.

"Well I think the vote count itself clearly indicates that there is not a one third plus one minority to sustain a presidential veto yet. Perhaps they'll get there. But the longer this deal is reviewed by the American people and they learn details like Qassem Suleimani and the Qudds Force and the Revolutionary Guard corps getting sanctions relief, or the fact that it may take at least 24 days if not weeks to get access to disputed sites. I think the American people are going to weigh in and Congress is going to reflect their opinion and that we're going to kill this deal," he said.

But Democratic Senator Dick Durbin said that Senator Kerry made a convincing case for the agreement's passage.

"Iran, under this agreement, will have to dramatically dismantle the technology they've developed for nuclear weapons and they will have to retire in a dramatic fashion the stockpile of fissile material that could be used for the development of weapons. Its my belief that this agreement is in the best interest of the United States security and the security of the Middle East.

"Its an agreement which was carefully crafted with our allies at the table, it brought Iran to the table facing sanctions which obviously had a dramatic impact on their economy. We need to seize this moment to make the Middle East safer and to make the world safer," he said.

Both Washington's Gulf allies and Israel have lobbied hard against the deal, worried that it may end Iran's isolation and empower it strategically at their expense.