A top Iranian official said on Wednesday that Tehran could consider working with the United States over the crisis in Iraq if talks on its nuclear programme are successful.

Asked about possible cooperation in Iraq, President Hassan Rouhani's chief of staff Mohammad Nahavandian told reporters in Oslo that the nuclear talks were a "test for confidence building".

"If that comes to a final resolution, then there might be opportunities for other issues to be discussed."

The rise of the jihadist Islamic State in Iraq and the Levant (ISIL), which has made sweeping gains in northern Iraq in recent days, has raised speculation over cooperation between Washington and Tehran to help stop the insurgency.

And on Monday, US Deputy Secretary of State William Burns held a brief meeting with Iranian officials in Vienna on the sidelines of the nuclear talks.

Nahavandian said he was opposed to any foreign intervention in Iraq unless it was requested by the government, but also criticised US inaction.

"The outside world should just respond to what the government of Iraq wants (and) should not intervene in the management of the situation.

"With regards to the United States, we have not seen any serious action from them against this wave of terrorism inside Iraq."

Rouhani said Wednesday that Iran would do whatever it takes to protect revered Shiite Muslim holy sites in Iraq against the Sunni ISIL militants.

Meanwhile, Nahavandian said he believed a July 20 deadline for Iran and world powers to reach a deal on Tehran's nuclear drive could be met.

"There are many people around the world who look optimistically to the ongoing negotiations and I am not an exception to that rule," he said.

Tehran, world powers begin drafting nuclear deal: Iran FM
Tehran (AFP) June 18, 2014 - Iran and world powers started drafting Wednesday a comprehensive nuclear agreement but still face many sticking points, Iranian Foreign Minister Mohammad Javad Zarif said.

"Today we have slowly begun to draft the final agreement... but there are still many differences" over the text, ISNA news agency quoted Zarif as saying from Vienna.

"This does not mean we have reached an agreement," said Zarif, according to IRNA news agency.

"Fundamental disagreements" continue to divide Iran and the P5+1 powers -- Britain, China, France, Russia and the United States plus Germany -- he said.

But Zarif said the two sides have agreed on a title for the text, which will be known as the "General Joint Plan of Action."

A new round of negotiations between Iranian diplomats and those of the six powers that opened Monday in Vienna had been "very difficult" so far.

The talks, which run through Friday, are aimed at clinching a comprehensive nuclear deal by a July 20 deadline set up by an interim agreement.

Iran's top negotiator Abbas Araqchi earlier told IRNA news agency that Iran hoped to settle all differences with the six powers by the target date.

The main sticking points are the timetable for a full lifting of crippling US and EU sanctions, and the scale to which Iran would be allowed to continue uranium enrichment, he said.

Enrichment is the sensitive process at the centre of Western concerns about Iran's nuclear ambitions, as it can produce both fuel for nuclear power stations and, in highly extended form, the core of an atomic bomb.

The P5+1 want Iran -- which insists its nuclear drive is purely for civilian use -- to drastically reduce its uranium production capacity, and keep only a few hundred centrifuges active.

They want to ensure that Iran's nuclear activities are purely peaceful. In return, Iran wants the removal of international sanctions that have choked its economy.

In the remarks to IRNA, Araqchi said "it won't be a catastrophe" if the July 20 target date is not met.

"We hope to start work on Wednesday on drafting the text of a final agreement, not the big issues but the general framework and the introduction," Araqchi said.

"There is a still a long way to go before we reach an agreement acceptable to all sides."

An interim deal struck last November led the six powers to release $7 billion from frozen funds in return for a slowdown in Iran's controversial uranium enrichment.

Iran began implementing the November deal in January.