The head of the UN atomic watchdog called Monday for fresh guidance from member states on how to jumpstart its stalled probe into Iran's suspected suspected nuclear weapons drive.

The International Atomic Energy Agency "will continue to address the Iran issue through dialogue and in a constructive spirit," Yukiya Amano told a closed-doors regular meeting of its 35-nation board of governors in Vienna.

"The views of member states are of vital importance in finding a solution."

In a report sent to IAEA member states ahead of this week's meeting, Amano said that after two fruitless trips to Iran by chief inspector Herman Nackaerts, on January 29-31 and February 20-21, "major differences" with Tehran remained.

Iran turned down IAEA requests for the team to visit the Parchin military site near Tehran where a November agency report said suspicious high-explosives tests consistent with developing nuclear warheads were carried out, Amano said Monday.

He said that the IAEA had evidence of unspecified ongoing "activities" at Parchin, meaning that "going there sooner is better than later". Western diplomats suspect Iran is removing evidence from the site.

Amano revealed that Iran had offered Nackaerts's team access to another military site in the northwest region of Marivan mentioned in the November report, but "only a few hours" before they were due to leave.

The new report also said Iran had substantially ramped up the enrichment of uranium, in defiance of multiple UN Security Council resolutions, to 20-percent purity. Uranium enriched to 90 percent can be used in a nuclear bomb.

Western powers hoped to convince Russia and China to back a strong resolution by the IAEA board this week condemning Tehran, diplomats said, but it was unclear that they could convince others, most notably China and Russia.

Instead, discussions are expected to focus on hopes for a resumption of talks between Iran and the P5+1 powers -- the permanent members of the UN Security Council the United States, China, Russia, Britain and France plus Germany.

The November report by the IAEA substantially raised suspicions of a covert Iranian nuclear weapons programme, stoking speculation that Israel may try to knock out Iran's sprawling network of nuclear sites with air strikes.

Obama, due to meet Israeli Prime Minister Benjamin Netanyahu later Monday, said Sunday there had been "too much loose talk of war", insisting that sanctions were biting but again warning Iran that military force was not ruled out.

Amano reiterated to the board of governors meanwhile that Washington's announcement last week of a deal with North Korea involving Pyongyang suspending sensitive nuclear activities was "an important step in the right direction."

Amano said the agency could travel at short notice.

But he stressed that he was awaiting further details, and that with the IAEA denied access to North Korea since 2009, the agency's "knowledge of the country's nuclear programme is limited."

"It is not yet time to have direct contact with North Korea, and we do not have any invitation from North Korea," he told reporters. "We need intensive consultation with North Korea and sending a high-level mission is not excluded."

On Syria, Amano said that in a February 20 letter Damascus "asked for understanding of 'the difficult circumstances and the delicate situation Syria is passing through,'" in reference to the current unrest.

The IAEA board reported Syria to the UN Security Council last year over a site allegedly bombed by Israel in 2007 that the agency believed was "very likely" a covert nuclear reactor. Syria has denied the accusations.