A week of Iran's nuclear talks ended with a deadlock over sensitive atomic research and the lifting of sanctions, talks will resume next week. (Reuters)

The latest round of talks over Iran’s nuclear future ended abruptly Friday with negotiators planning to resume discussions next week in a last-ditch effort to forge an agreement by a March 31 deadline.

The immediate explanation for the talks ending was that the Iranians had to return to Tehran for the funeral of Sekineh Payvandi, the 90-year-old mother of President Hassan Rouhani and his brother, Hossein Fereydoun, who is a member of the team negotiating Iran’s nuclear program with six world powers, including the United States.

Word of Payvandi’s death reached the negotiators Friday morning just before negotiations were to take place. The Iranian media carried many photographs of Secretary of State John F. Kerry, sympathy evident on his face, moving toward a clearly grief stricken Fereydoun, who appeared on the verge of tears over his mother’s death. Both men had their arms outstretched for a hug.

The photo of them in a near-embrace could pose problems for Rouhani from the hardliners who oppose him and the nuclear negotiations.

Earlier this year, when Iranian Foreign Minister Mohammad Javad Zarif was photographed strolling across a bridge in Geneva with Kerry, hardliners accused Zarif of walking with the enemy.

President Obama addressed the people of Iran in a message celebrating Nowruz, the Iranian New Year, and said that this year represented the “best opportunity in decades” for the two countries to pursue a different relationship. (Reuters)

It is unclear why the entire negotiating team had to leave for the funeral, apart from Fereydoun, who almost immediately flew to Tehran upon hearing of his mother’s death.

Initially, the talks had been scheduled to break Friday, anyway, so the Iranians could return home to celebrate the new year, Nowruz, one of the most important days in the Iranian calendar.

But despite some progress over four days of talks, many fundamental issues remain unresolved. So the negotiators had considered staying and continuing their talks through at least Saturday, when the foreign ministers of France, Britain and Germany were expected to come to Lausanne for consultations. Those tentative plans were upended by Payvandi’s death.

The United States, Europeans and the Iranians held some abbreviated discussions on Friday morning, their fifth day of trying to reach a framework agreement to constrain Iran’s nuclear program and ease sanctions.

Outside the negotiating room there was a traditional Nowruz table laden with sweets, stuffed animals and a pot of grass. The message seemed to be that even an important holiday like Nowruz would not deter the negotiators from their task.

Now, Kerry plans to return to Washington on Saturday, stopping in London to consult with European allies in the talks. He said the nuclear talks would resume Thursday.

“We’ve had a series of intensive discussions with Iran this week, and given where we are in the negotiations, it’s an important time for high-level consultations with our partners in these talks,” said Marie Harf, the State Department’s deputy spokeswoman.

Graphic: Iran's potential nuclear capability

Kerry also spoke by phone with the foreign ministers of China and Russia, the other two countries negotiating alongside the United States.

Next week will be the final chance for negotiators to come up with a general agreement before their self-imposed deadline, leaving three months to work out technical details.

The West and its allies fear that Iran’s uranium enrichment program could eventually produce material for a nuclear weapon. Iran insists it does not seek nuclear arms and only wants reactors for energy and medical applications.

Diplomats familiar with the negotiations say that they have not settled on ways to ensure that Iran’s nuclear program is used solely for peaceful purposes.

For example, they haven’t even agreed on how many centrifuges Iran will be allowed to operate to enrich uranium, though discussions are centering on about 6,000. It’s also unclear whether Iran can use only centrifuges with outdated technology from the 1970s or more efficient centrifuges developed by Iranian technicians but not yet in operation.

Nor have they agreed on the pace at which sanctions might be lifted by the United States, the United Nations and the European Union. Iran demands an immediate lifting of sanctions, said a U.S. official, while the other nations are insisting on a gradual pace linked to Iran’s willingness to open up its facilities to international inspections and comply with other elements of an agreement.

President Obama and Kerry urged Iran’s leaders to strive for an agreement in the spirit of Nowruz.

Obama, in his annual videotaped Nowruz message, said this opportunity may not come again soon.

If Iran’s leaders do not agree to a reasonable deal, Obama said, the country will remain isolated and sanctions will further squeeze its economy, which has suffered a double blow from falling oil prices.

But if a deal can be forged, he said, Iranians will enter a world of more job opportunities, travel abroad and cultural exchanges.

“In other words, a nuclear deal now can help open the door to a brighter future for you, the Iranian people, who, as heirs to a great civilization, have so much to give to the world,” he said.

Obama also called Friday for the release of four Americans detained or missing in Iran, arguing that the start of Nowruz offers an opportunity for the Iranian government to reunite them with their families.

Invoking the holiday, Obama asked Iranian leaders to free Christian pastor Saeed Abedini, former U.S. Marine Amir Hekmati and Washington Post reporter Jason Rezaian, as well as locate missing American investigator Robert Levinson.

“The spirit of family is deeply woven into all of the rich cultural traditions of the Nowruz holiday,” the president said in a statement. “It is a time for reuniting and rejoicing with loved ones and sharing hopes for the new year. Today, as families across the world gather to mark this holiday, we remember those American families who are enduring painful separations from their loved ones who are imprisoned or went missing in Iran.”

Kerry also issued a statement tying the nuclear talks to the hope symbolized by the Persian new year.

The Iranians, however, say the onus for the tough political decisions falls on Washington and its allies.

Zarif tweeted a message in response to Obama’s Nowruz greeting, saying, “Iranians have already made their choice: Engage with dignity. It’s high time for the U.S. and its allies to choose: pressure or agreement.”

Juliet Eilperin contributed to this report from Washington.

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