BRUSSELS/TEHRAN, March 17 -- Prospects for a landmark framework agreement on Iran's nuclear program between Tehran and six major powers remain murky as a late March deadline closes in.

"We're still making progress but there is a long way to go if we're going to get there," British Foreign Secretary Philip Hammond said, after talks on Monday in Brussels with his French, German and Iranian counterparts plus European Union foreign policy chief Federica Mogherini.

The talks were aimed at narrowing gaps in the positions between Iran and the world powers, as part of a prolonged negotiating process that could get Tehran to curb its nuclear activities for at least 10 years in exchange for the gradual lifting of the international community's economic sanctions on Iran.

The P5+1 group, namely Britain, China, France, Germany, Russia and the United States, has been negotiating with Iran over its nuclear plan since mid-2013, and hoped to reach a final agreement by the end of March.

Iran claims its nuclear program is for peaceful purposes, but many in the West fear the country could eventually develop an atom bomb.

"It's always useful to talk but we, the French, want a solid deal," French Foreign Minister Laurent Fabius said.

"Certain points are yet to be resolved, we hope we will be able to resolve them but as long as it's not done, it's not done," Fabius said.

Mogherini, who is negotiating with Iran on behalf of the world's five nuclear powers and Germany, said Monday that her talks with Iranian Foreign Minister Mohammad Javad Zarif will contribute to advancing the process on Iran's nuclear deal.

After the meeting, Mogherini and the three European foreign ministers stressed their determination to work toward an agreement with Iran on a solution that would address all concerns of the international community over the Iranian nuclear program, according to an EU press release.

"This was a useful meeting and I am confident it will contribute to advancing the process in the coming days and weeks," Mogherini said, adding that all sides were aware how important it is to seal a good deal.

However, Mogherini also said that it was not clear whether "a technical solution" to fill the remaining gaps can be found.

"I see the elements for a deal to be reached but I still see the gaps that need to be filled."

Before the Iranian delegation headed to Brussels for meetings with European ministers, Zarif and U.S. Secretary of State John Kerry held nearly five hours of talks in the Swiss city of Lausanne, struggling to narrow gaps on some aspects of the country's nuclear issue.

"Solutions in some areas are within reach. But we are still far apart in some other areas," Zarif was quoted as saying by state IRIB TV.

The bilateral talks covered myriad topics, including sanctions against Iran and technical aspects of the nuclear program. "We need to continue the talks with all sides till Friday and wait for the outcome," Zarif said.

On Monday, senior Iranian negotiator Abbas Araqchi said differences remain in both technical and political issues in the intensive talks.

"In general, the talks on Monday were satisfying. There is hope that this round of talks would end with some progress," Araqchi was quoted as saying by IRIB.

Iranian Parliament Speaker Ali Larijani said Monday that he is optimistic about the results of ongoing nuclear talks.

"I am not pessimistic about a deal and it is highly likely, since many steps have already been taken in this direction," Larijani said.

Iran may accept further monitoring missions on its nuclear program, provided that Iran's nuclear dossier is returned to the International Atomic Energy Agency by the UN Security Council, the Iranian speaker said.

He supported a statement signed by 260 lawmakers Monday regarding the feasibility of a deal from the Parliament's perspective.

The statement called for these two conditions: the removal of all sanctions against the country and normalization of Iran's nuclear dossier.

The statement urged Iranian nuclear negotiators to protect what it called the country's nuclear achievements. It warned that in the event the other party breaches its contract once an agreement is reached, the deal will be suspended and Iran will start uranium enrichment at any level it desires.