DOHA - A nuclear deal with Iran will significantly reduce Tehran's enrichment capacity, US Vice-President Joe Biden's national security adviser told a conference in Qatar on Monday.

Dr Colin H. Kahl, speaking at the US-Islamic World Forum in Doha, said the current deal being hammered out was the best on offer, despite many sceptical voices in the US and elsewhere, including Gulf Arab states.

"Under the deal we are negotiating... Iran's enrichment capability will be substantially rolled back," said Kahl.

"The deal we are negotiating makes us and the region safer."

The ongoing talks to finalise a nuclear accord between Iran and world powers, including the United States, are deadlocked weeks ahead of a deadline.

Negotiations at the weekend in Geneva, Switzerland, failed to bridge differences between Washington and Tehran, especially over the crucial issue of inspections of military sites.

Other sticking points remain, including the possible military dimensions of the Iranian nuclear programme and the demands by the P5+1 group for UN inspections of Iranian military bases.

A deadline has been set for June 30 to reach a ground-breaking agreement that would see Iran curtail its nuclear ambitions in return for a lifting of crippling international sanctions.  (AFP)