U.S., European negotiators meet in London for Iran talks

European and U.S. negotiators are meeting in London on Saturday ahead of a March 31 deadline for a political framework agreement, and a full nuclear deal by June 30.

France's foreign minister said on Saturday that his country wanted an agreement over Iran's nuclear program that was sufficiently robust to guarantee that Tehran could not acquire an atomic bomb.

U.S. Secretary of State John Kerry told reporters that the talks "have made substantial progress, though important gaps remain."

Iran and six Western countries — the United States, Britain, France, Germany, Russia and China — suspended negotiations on a nuclear agreement on Friday in Lausanne, Switzerland to enable members of the Iranian delegation to attend the funeral of Iranian President's Hassan Rouhani's mother in Tehran. They are set to meet again next week to break a deadlock over sensitive atomic research and lifting of sanctions.

French negotiators have been demanding more stringent restrictions than the other Western delegations on any potential deal reached with Iran. France raised last minute objections to an interim agreement reached with Iran in 2013, and could threaten a deal again, officials said. It is particularly opposed to providing Iran with quick relief from international sanctions and wants a longer timeframe for restrictions on Iran's nuclear activity.

Top Russian negotiator Sergey Ryabkov and Iran's atomic energy chief Ali Akbar Salehi said in recent days that the technical work of an agreement was nearly done.

In Tehran, Iranian President Hassan Rouhani was optimistic. "Achieving a deal is possible," he said. "There is nothing that can't be resolved."

Iran denies allegations from the Western countries and their allies that it harbors nuclear weapons ambitions. It wants all U.N. sanctions to be lifted immediately, including those targeting its nuclear program.

While the talks have made progress over the past year, the differences are still wide enough to potentially prevent an agreement in the end. Officials told the Associated Press that the U.S. and Iran were drafting elements of a deal that commits the Iranians to a 40 percent cut in the number of machines they could use to make a nuclear weapon. In return, Iran would get quick relief from some crippling economic sanctions and a partial lift of a U.N. embargo on conventional arms.

The sides ultimately want to reach a full agreement by June 30.

But both the U.S. and Iran face pressure to come up with the main contours of a deal by this month's end, with President Barack Obama and Iran's Ayatollah Ali Khamenei having spoken against extending negotiations for the third time.

EU foreign policy chief Federica Mogherini denied on Friday that there were divisions between Europe and the United States.

"There is unity, there is unity on the fact that we want a deal, we want a good deal," she said in Brussels after talks with French President Francois Hollande, German Chancellor Angela Merkel and British Prime Minister David Cameron.

Iran's Deputy Foreign Minister Abbas Araqchi said the talks would resume on Wednesday.

Al Jazeera and wire services