The US secretary of state and his Iranian counterpart have held four hours of nuclear talks in Switzerland, after which the Iranian delegation headed to Brussels for meetings with European ministers.

Monday's meeting in Lausanne between John Kerry and Mohammad Javad Zarif is part of a diplomatic push by the two sides to come up with the outlines of an agreement by the end of March.

A full accord is due by July 1.

"If [Iran's nuclear programme is] peaceful, let's get it done. And my hope is that in the next days, that will be possible," Kerry told American CBS television on Sunday.

There were, however, "important gaps", he said.

The meeting between Kerry and Zarif included Ernest Moniz, US energy secretary, and Ali Akbar Salehi, Iran's nuclear chief, who also met on Sunday to negotiate technical details of Iran's nuclear programme.

"I'm very optimistic," Salehi said afterwards, leaving Zarif and Kerry in the room for a one-on-one meeting.

Six world powers, the US, Germany, France, Britain, Russia and China, are trying make a deal with Iran that would curb Iran's most sensitive nuclear activities for at least 10 years in exchange for the gradual easing of some sanctions.

Talks in Brussels

After their meeting in Brussels, the Iranian delegation will return to Lausanne for more talks with the Americans, and will be joined later in the week by European ministers.

The West, Israel and Gulf Arab countries suspect Iran of ambitions to create an atomic weapon. Iran denies that accusation and says its research is for purely peaceful purposes.

The US and Iran have not had diplomatic relations for 35 years but the 2013 election of President Hassan Rouhani resulted in a minor thaw and a diplomatic push to resolve the more than decade-old nuclear standoff.

Under a November 2013 interim deal with the six world powers, Iran stopped expanding its activities in return for minor sanctions relief.

Since then the parties have been pushing for a lasting accord, amid the alarm of Israel, US Republicans and Gulf Arab states warning the US administration over a bad deal.

On Monday, a senior Saudi prince said that any terms that world powers grant Iran under a nuclear deal will be sought by Saudi Arabia and other countries, risking wider proliferation of atomic technology, according to BBC.

"I've always said whatever comes out of these talks, we will want the same," Turki al-Faisal said.

He has previously served as head of Saudi intelligence and Riyadh's ambassador to Washington and London but is no longer a government official.

Al jazeera