Secretary of State John F. Kerry, left, talks with British Foreign Secretary Philip Hammond as they meet with foreign ministers from China, France and Germany in Vienna on Monday. (Pool photo by Carlos Barria/via AP)

Nuclear talks with Iran could stretch beyond Tuesday’s extended deadline, as the parties try to resolve key issues involving sanctions, Iran’s nuclear research, and the fate of embargoes on the sale of missiles and weapons to Tehran.

A senior Iranian official said Monday that his delegation considers Tuesday an “artificial deadline” for a nuclear agreement, but indicated that Iran expects a move to lift United Nations prohibitions on the sale of conventional weapons and ballistic missiles.

Iran has long maintained that an arms embargo imposed in 2010 is illegal because it has nothing to do with nuclear weapons. The official said Iran is not insisting that the embargo be part of a comprehensive agreement, but he also said that lifting it would be a “natural consequence” of any agreement involving restrictions on Iran’s nuclear program in exchange for sanctions relief.

“This is one of the important issues we are discussing,” said the official, a negotiator who spoke to Western reporters on the condition of anonymity.

The remarks suggest a new wrinkle in the talks on the eve of Tuesday’s extended deadline.

The U.S. delegation made no public statements Monday.

A U.S. “fact sheet” outlining a political framework agreement reached with Iran three months ago said nuclear-related U.N. sanctions on Iran would be lifted. In their place, a new umbrella resolution would be introduced to incorporate remaining
non-nuclear sanctions, including on conventional weapons and ballistic missiles, and the transfer of sensitive technology.

An Iranian fact sheet at the same time said that “all” U.N. sanctions would be lifted, and did not mention existing non-nuclear sanctions.

In his remarks to reporters Monday, the Iranian negotiator was unclear about whether an agreement to end the arms embargo must accompany a nuclear deal.

He said Iran expects a “fundamental shift” in the U.N. Security Council’s approach to Iran, which he characterized as being “terrible, to put it mildly.”

“There cannot be a resolution to the nuclear issue, and at the same time those sanctions continue to exist,” he said. “We understand it’s a hard decision they have to make. If they want to get the job done, if they want to open a new page in relations with Iran, they have to make this hard choice.”

Foreign ministers from Britain, China, France, Germany and Russia arrived in Vienna early Monday, hoping to seal a deal. The ministers met separately with one another and, late in the afternoon, as a group with the Iranian delegation.

All of the meetings were held behind closed doors. Except for the Iranian briefing, Chinese Foreign Minister Wang Yi was among the few diplomats who made any public statement here Monday.

“What is important is that today and tomorrow, all parties, especially the United States and Iran, should make their final decisions as quickly as possible,” he told reporters.

The Iranian negotiator said all of what he called the remaining “difficult” decisions were up to the United States and its partners.

“We believe that if there are not extra demands, if our counterparts are prepared to choose cooperation and agreement, as opposed to coercion, we can get the matter done in the next few days,” he said. “I suppose the choice is theirs.”

His remarks were a direct response to Secretary of State John F. Kerry, who on Sunday said that it was Iran that had “hard choices” to make and that the United States was prepared to walk away without a deal if Iran showed “absolute intransigence.” U.S. officials have characterized the talks as being in the “end game.”

In recent days, Kerry has cautioned against overoptimism and warned that the talks could fail.

“Still nothing is clear,” Iranian Foreign Minister Mohammad Javad Zarif said in passing remarks to some of the hundreds of reporters camped outside Vienna’s Coburg Palace hotel, where the talks are being held. “Some differences remain and we are trying and working hard.”

The senior Iranian negotiator alluded to the Obama administration’s desire to have a final deal ready to present to Congress by the end of Thursday for a 30-day review.

If an agreement arrives at Congress after that, the review period will grow to 60 days, potentially increasing political difficulty for the White House in avoiding a resolution of disapproval by lawmakers. Although Obama has the power to implement the deal himself, including waiving legislative sanctions, he has agreed not to act before the review is complete.