Key players in talks on Iran’s nuclear programme have warned of big gaps between Iran and world powers, with only a week left to strike a deal.

Arriving in Vienna for the talks, US Secretary of State John Kerry said “significant differences” remain – a view echoed by France and the UK.

An Iranian envoy also said it was not clear if major gaps could be bridged.

The talks seek to persuade Iran to limit its nuclear programme in exchange for the lifting of sanctions.

Discussions on Sunday have been inconclusive.

“We haven’t made the decisive breakthrough,” said the UK’s Foreign Secretary, William Hague. “There are very significant gaps.”

There is growing speculation that the 20 July deadline for an agreement will need to be extended.

An interim deal was reached last year. However, the parties have been unable to reach agreement on imposing long-term restrictions over Iran’s uranium enrichment and plutonium production – processes that could yield material for nuclear warheads.

World powers suspect Iran is seeking atomic weapons. Iran strongly denies the charge, insisting that it is enriching uranium to fuel its power plants, and for medical needs.

A deal could see the lifting of oil and trade sanctions on Iran.