The head of the UN's nuclear agency, Yukiya Amano, has warned it will "take some time" before work can begin on verifying whether Iran is complying with a deal on its nuclear programme.

Iran agreed last week to curb some nuclear activities for six months in return for sanctions relief.

The deal requires increased UN inspections of Iran's nuclear sites including the Arak heavy water plant.

Mr Amano said he could not yet tell when the inspections would begin.

Under the international deal, Iran will receive some $7bn (£4.3bn) in sanctions relief while talks continue to find a more permanent agreement.

The BBC's Bethany Bell in Vienna says that the stipulated six-month interim period will only begin once technical issues such as inspections have been worked out.

The accord, reached in Geneva on Sunday with the US, UK, France, Russia, China and Germany, has been generally welcomed.

But Israeli Prime Minister Benjamin Netanyahu has called it a "historic mistake" and some US senators say it is too soft.
'Funding implications'

The West has long suspected that Iran's uranium enrichment programme is geared towards making a weapon, but Tehran insists it only wants nuclear energy.

The Vienna-based International Atomic Energy Agency (IAEA) is expected to play a key role in verifying Iran's compliance, including significantly expanding its inspections of nuclear sites.

But Mr Amano told reporters on Thursday: "It will take time because it is a quite complicated task and we would like to properly prepare and do the job properly.

"I cannot tell when we will be ready."

He indicated that the agency would be seeking special funding for the operation, which he said would "requires a significant amount of money and manpower".

"The IAEA's budget is very, very tight. I don't think we can cover everything from our own budget."
Plutonium fears

Earlier on Thursday, as part of the deal, Iran invited Mr Amano to visit its Arak heavy water plant on 8 December.

The purpose of the facility is to provide heavy water to help control the nuclear activity of fuel rods in the reactor, which is still under construction.

Western powers fear the reactor could be used to make weapons-grade plutonium, but Iran says it will make medical isotopes.

Under Sunday's deal, Iran agreed not to commission the Arak reactor or transfer fuel or heavy water to the site.

The IAEA regularly visits a nearby research reactor site but has not been at the heavy water plant since August 2011 despite repeated requests.

The visit is the first concrete step taken under the IAEA plan, a "joint statement on a framework for co-operation" signed with Iran on 11 November.

Also on Thursday, Mr Amano said that satellite images of North Korea - another state whose nuclear activities have raised international alarm - indicated it was trying to restart a previously decommissioned nuclear reactor.

The Yongbyon plant - widely believed to be capable of producing weapons-grade plutonium - was shut down in 2008 amid international talks, but North Korea announced in April that it would restart it.

The IAEA has no access to the site, so Mr Amano said it was "not possible for us to conclusively determine whether the reactor has been restarted".

BBC