World leaders are racing against the clock to finalize the details of a preliminary deal with Iran over its nuclear capabilities. Several issues still divide negotiators as Tuesday's deadline looms.
Foreign ministers from the United States, the United Kingdom, Germany, France, China and Russia are continuing meetings with Iranian officials in the Swiss town of Lausanne well into the night on Monday, in an effort to finalize a draft accord over the Islamic republic's nuclear facilities.
The so-called P5+1 group have set a deadline of midnight on Tuesday to come to a consensus on the outlines of a deal.
They will then have until June 30 to officially finalize it.
US Secretary of State John Kerry said that they would continue talks as long as was necessary.
"There still remain some difficult issues. We are working very hard to work those through. We are working late into the night and obviously into tomorrow," he said.
Acting State Department Spokeswoman Marie Harf said although they were aiming to meet the deadline, there was still room to move.
Meanwhile China's Foreign Minister Wang Yi said he was "cautiously optimistic" a deal would go through, saying the differences between the powers were "narrowing."
Despite this, Russian media reported that Russian Foreign Minister Sergey Lavrov left the talks early, with a spokeswoman saying he will only return if there is a "realistic" chance of a deal.
Iran has already agreed to some measures such as lowering the number of uranium-enriching centrifuges it will be permitted to operate.
But disagreements persist over issues such as when the sanctions will be lifted, with Iran wanting them immediately terminated.
The world leaders involved in the negotiations say they would rather suspend the restrictions, so they can be reinstated if Iran breaks any terms, and only after the June 30 deadline has been reached.
Iran's Deputy Foreign Minister Abbas Araghchi said getting rid of sanctions was "very important to us for political and legal reasons."
The accord's time limit is also causing friction.
While the Middle Eastern nation wants the agreement to last for 10 years, other leaders are pushing for at least 15.
Germany's Foreign Minister Frank-Walter Steinmeier said on Monday that this was the least of their problems.
"The issue here is more than 10 years. We have more ambitious expectations," he said. "Talks are without a doubt in a difficult phase right now."
Global reactions to the proposed deal have been mixed, with Israeli Prime Minister Benjamin Netanyahu describing the idea as tantamount to "rewarding" Iran for its current military operations in Yemen.
Saudi Arabia, who has been carrying out airstrikes on Iran-backed fighters in Yemen for the past five days, has also expressed skepticism.
P5+1 officials also want Iran to agree to widespread inspections of its remaining facilities by the UN's atomic watchdog.
an/bk (AP, AFP, Reuters, dpa)