DHAKA: Doubts are growing that Monday’s deadline for a deal on Iran's controversial nuclear program will be met at talks in Vienna in Austria.

Both the US and Germany said the sides were working to close ‘big gaps’, with some suggestions that the deadline could be extended, reports the BBC.

Six world powers want Iran to curb its nuclear program in return for the lifting of United Nations sanctions.

Iran rejects claims that it is seeking to build nuclear weapons.

It says its program is purely peaceful for energy purposes.

Representatives of the so-called P5+1 group - Britain, China, France, Russia, the US plus Germany - are taking part in the negotiations with Iran in the Austrian capital.

On Saturday, US Secretary of State John Kerry said, ‘We’re working hard. We hope we’re making careful progress, but we have big gaps... which we’re working to close’.

He spoke after postponing his trip to Paris in order to meet Iranian foreign minister Mohammad Javad Zarif - their fourth talks in three days.

German Foreign Minister Frank-Walter Steinmeier called the negotiations so far ‘constructive’, but added, ‘That must not mask the fact that there is still a big gap between us in many aspects’.

BDST: 1237 HRS, NOV 23, 2014