Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif
Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif Reuters

A United States official said on Monday that some progress was made in talks with Iran on its nuclear program, though both sides said much remained to be done, according to the Reuters news agency.

Negotiators from Iran and six major powers agreed to resume talks next Monday at a venue to be decided, the American official said, speaking after U.S. Secretary of State John Kerry and Foreign Minister Mohammad Javad Zarif held two-day talks in Geneva.

Zarif told Iran's Fars news agency, "We had serious talks with the P5+1 representatives and especially with the Americans in the past three days ... But still there is a long way to reach a final agreement."

An Iranian source told Reuters that Zarif and Kerry would return to the Swiss city to launch the next round on March 2.

The United States, Russia, China, Britain, France and Germany are seeking to negotiate an agreement with Tehran to address concerns that Iran is seeking nuclear weapons technology, something it denies.

"These were very serious, useful and constructive discussions. We have made some progress but we still have a long way to go. We did very much sharpen up some of the tough issues so we can work to resolution," the senior U.S. administration official told reporters, according to Reuters.

While negotiators hope to meet a self-imposed March 31 deadline for an initial political deal, the official added that would not "make us rush to an agreement that does not fulfill the objectives that the president has given to us."

The aim of ensuring Iran does not acquire a nuclear weapon "has to be met and that is not about the deadline, it is about the purpose", the official said.

Diplomats who spoke to Reuters said the Western powers aim for a deal lasting at least 10 years under which Iran would need at least one year to produce enough highly enriched uranium for a single nuclear bomb, the so-called "breakout" capacity.

"We have always said we will have a one-year breakout time for a double digit number of years and that remains the case," the senior U.S. official said on Monday.

The sides reached an interim deal in November of 2013, under which Iran committed to limit its uranium enrichment to five percent and is gradually winning access to $4.2 billion of its oil revenues frozen abroad and some other sanctions relief.

The talks were supposed to continue in order to turn the interim deal into a permanent one. However, the talks have stalled and two deadlines for a final deal have been missed, with a third one looming on July 1