US Secretary of State John Kerry during testimony to members of the House of Representatives on Iran's nuclear program on Wednesday. Credit:AP "From the agreement that is forming it appears that they have given up on that commitment and are accepting that Iran will gradually, within a few years, develop capabilities to produce material for many nuclear weapons," said Mr Netanyahu. "They might accept this - but I am not willing to accept this." To date US negotiators have sought to hammer out a deal that would see the so-called "breakout time" – the time Iran would need to create a nuclear weapon should it break conditions of the agreement – to a year or more. Such a timetable is considered necessary to allow an international coalition time to respond with sanctions or even military force if Iran breaks agreements. Negotiators from both sides have had their task complicated by hardliners in Tehran and Washington.

Iran's Supreme Leader Ayatollah Ali Khamenei during a ceremony at the Military College of Tehran. Credit:New York Times Some of the most strident voices in Washington have come from members of Congress known for their particularly strong support of Israel and the right-wing government of Benjamin Netanyahu. Some fear Mr Obama is so keen to secure a significant foreign policy achievement before he leaves office that his officials are negotiating from a weak position. The White House has denied reports that any deal with Iran would last for only 10 years. US officials had previously said they wanted the agreement to last for a "double-digit" period. Mr Netanyahu is set to visit the US next week to address Congress at the invitation of the Republican Speaker of the House, John Boehner. The address was organised without the knowledge of US President Barack Obama.

The visit is controversial not only due to the apparent snubbing of the President, but because the White House has a practice of not appearing to endorse leaders facing elections, as Mr Netanyahu does in three weeks. Critics of the Israeli prime minister's visit from both countries have argued it is dangerous for the Congress to pursue its own "freelance" foreign policy, and also for the alliance between the two nations to be conflated with the relationship between Mr Netanyahu's Likud Party and the Republican Party. On Wednesday Mr Obama's chief diplomat, Secretary of State John Kerry, questioned Mr Netanyahu's foreign policy judgment as he testified before a Republican-dominated foreign affairs committee in the House of Representatives. Referring to Mr Netanyahu's condemnation of the Iran talks, Mr Kerry said with clear irony: "The Prime Minister was also profoundly forward-leaning and very outspoken about the importance of invading Iraq under George W. Bush." He also rejected Mr Netanyahu's criticism of earlier temporary deals with Iran, saying: "Israel is safer today with the added time we have given and the stoppage of the advances in the nuclear program than they were before we got that agreement - which, by the way, the prime minister opposed. He was wrong."

A day earlier Mr Obama's national security adviser, Susan Rice, was even more pointed in her criticism of Mr Netanyahu. She told the PBS interviewer Charlie Rose that the visit just before the election had "injected a degree of partisanship, which is not only unfortunate, I think it's destructive of the fabric of the relationship". "I'm not going to ascribe motives to the prime minister," she said, "The point is, we want the relationship between the United States and Israel to be unquestionably strong, immutable, regardless of political seasons in either country, regardless of which party may be in charge in either country." On Wednesday, White House spokesman Josh Earnest endorsed Dr Rice's statement. "Her comments are entirely consistent with what the President has already said," he said. Mr Obama will not meet with Mr Netanyahu, whose address coincides with the last days of negotiations with Iran. During the visit of German Chancellor Angela Merkel earlier this month, Mr Obama said: "We have a practice of not meeting with leaders right before their elections, two weeks before their elections.

"As much as I love Angela, if she was two weeks away from an election she probably would not have received an invitation to the White House — and I suspect she wouldn't have asked for one." Earlier this week, Mr Netanyahu said that if the agreement was signed it would "allow Iran to become a nuclear threshold state. That is, with the consent of the major powers, Iran – which openly declares its intention to destroy the state of Israel – will receive a licence to develop the production of bombs. "It is my obligation as prime minister to do everything that I can to prevent this agreement; therefore, I will go to Washington to address the American Congress because the American Congress is likely to be the final brake before the agreement between the major powers and Iran." Mr Obama's Vice-President, Joe Biden, who also serves as president of the Senate, is one of several senior Democrats who have said they will not attend Mr Netanyahu's address. In turn, Mr Netanyahu has declined an invitation to meet privately with senior Democrats. with Telegraph, London