Talks on Iran's nuclear programme are entering a crucial weekend in Vienna, but there is no sign of a breakthrough as Monday, Nov 24 deadline looms, BBC News reports.

The U.S. admitted that "serious gaps do remain". But Secretary of State John Kerry did cancel plans to leave Austria, and held further talks with his Iranian counterpart Javad Zarif late on Friday.

Six world powers want Iran to curb its nuclear programme in return for the lifting of UN sanctions. The US, the UK, France, Germany, Russia and China - the so-called 5+1 group - are seeking reassurance that Iran is not trying to build a nuclear weapons capability. Tehran insists its nuclear programme is purely energy-related.

The P5+1 group and Iran reached an interim agreement a year ago. But the two sides failed to reach a lasting deal by July, as initially agreed, and extended the deadline until 24 November.

"We are running against the clock," White House spokesman Eric Schultz said on Friday. "Obviously, the deadline is Monday, and our folks there (in Vienna) are working furiously to meet it. Serious gaps do remain."

After meeting Kerry on Friday evening, Zarif said he heard "no new ideas" and had received "no remarkable proposals to take to Tehran".

Separately, the international nuclear watchdog, the International Atomic Energy Agency (IAEA), is calling on Iran to address its concerns about suspicious military activities that could be linked to a nuclear weapons programme.

A senior Iranian official told the BBC the team was expecting to reach an outline of a deal by the deadline and then spend the following seven-to-10 days working on the implementation of it at expert level.