VIENNA (Reuters) - An Iranian nuclear agreement is possible this week if Iran makes the "hard choices" necessary, but if not, the United States stands ready to walk away from the negotiations, U.S. Secretary of State John Kerry said on Sunday.
Speaking during a break from one of his four meetings with Iranian Foreign Minister Mohammad Javad Zarif on Sunday, Kerry said they had made "genuine progress" in talks over the last few days but "several of the most difficult issues" remain.
"If hard choices get made in the next couple of days, made quickly, we could get an agreement this week, but if they are not made we will not," he said in Vienna, where talks between Iran, the United States and five other powers are being held.
Foreign ministers from Britain, China, France, Germany and Russia began arriving on Sunday evening as the major powers make a push to meet Tuesday's deadline for a final agreement to end the 12-year-old dispute.
Kerry said negotiators were still aiming for that deadline, but other diplomats have said the talks could slip to July 9, the date by which the Obama administration must submit a deal to Congress in order to get an expedited, 30-day review.
The agreement under discussion would require Iran to curb its most sensitive nuclear work for a decade or more in exchange for relief from sanctions that have slashed its oil exports and crippled its economy.
U.S. President Barack Obama's administration, which has been accused of making too many concessions by Republican members of Congress and by Israel, remains ready to abandon the talks, Kerry said.
"If we don't have a deal and there is absolute intransigence and unwillingness to move on the things that are important for us, President Obama has always said we're prepared to walk away," he said.
European officials also said the onus was on Iran to cut a deal. After arriving in Vienna, French Foreign Minister Laurent Fabius told reporters the main question was whether Iran would make "clear commitments" on unresolved issues.
German Foreign Minister Frank-Walter Steinmeier said it would take courage and compromise to reach a deal. "I hope that this courage exists above all ... in Tehran," he told reporters.
The major powers suspect Iran of trying to develop a nuclear weapons capability. Iran says its nuclear program is solely for peaceful purposes such as producing medical isotopes and generating electricity.
The top U.S. and Iranian diplomats met for a sixth consecutive day on Sunday to try to resolve obstacles to a nuclear accord, including when Iran would get sanctions relief and what advanced research and development it may pursue.
Keeping up a what has been a steady stream of criticism, Israeli Prime Minister Benjamin Netanyahu said the United States and major powers were negotiating "a bad deal".
"It seems that the nuclear talks (with) Iran have yielded a collapse, not a breakthrough," he said, in remarks released by his office.
Iran's semi-official news agency Fars quoted an unnamed senior Iranian official as saying about 70 percent of a 32-page annex to the agreement had been written and "30 percent is between brackets", meaning it was still under discussion.
The agreement itself is expected to include a political understanding accompanied by five annexes.
"We hope that the main portion of this (annex) will be cleared up today, and if any issues remain, they will be discussed at higher-level meetings, so that we can reach a solution," the official said.
He said that issues under discussion include Iran's uranium enrichment facilities at Fordow and Natanz, its Arak heavy-water nuclear reactor under construction and research and development.
While they have made some progress on the type of bilateral sanctions relief that Iran may receive, the two sides remain divided on such issues as lifting United Nations sanctions and on its research and development of advanced centrifuges.
Diplomats close to the negotiations said they had tentative agreement on a mechanism for suspending U.S. and European Union sanctions on Iran.
But the six powers had yet to agree with Iran on a United Nations Security Council resolution that would lift U.N. sanctions and establish a means of re-imposing them in case of Iranian non-compliance with a future agreement.
In addition to sanctions, other sticking points include future monitoring mechanisms and a stalled U.N. probe of the possible military dimensions of past Iranian nuclear research.
Senior officials from the International Atomic Energy Agency, the U.N. nuclear watchdog, plan to visit Iran this week.
Another obstacle in talks is Iran's demand to be allowed to do research and development on advanced centrifuges that purify uranium for use as fuel in power plants or weapons.
Additional reporting by Louis Charbonneau in Vienna, Ori Lewis in Jerusalem, Krista Hughes in Washington and Firouz Sedarat in Dubai; Editing by Andrew Roche