The head of the UN nuclear watchdog said on Wednesday he was not confident there would be a breakthrough with Iran over the Islamic Republic's nuclear activities when talks resume later this week.

The International Atomic Energy Agency (IAEA) meets Iranian officials on Friday, more than two months after previous talks ended in failure, and is expected to seek to persuade Iran to address questions about its suspected nuclear weapons research.

"The reason I cannot be too optimistic is... we have been making our best efforts in a constructive spirit to work out an agreement between Iran and IAEA, but so far we have not been successful in reaching agreement," Yukiya Amano, IAEA Director General, told reporters during a visit to Helsinki. "I have no indication this will change very soon."

Iran denies accusations that it wants to develop nuclear weapon technology. But its refusal to limit and be more transparent about its nuclear activity has led to increasingly tough sanctions and sparked renewed speculation that Israel, Tehran's arch-enemy, might bomb Iranian nuclear installations.

Earlier on Wednesday, Britain's Telegraph newspaper reported that Iran's Supreme Leader Ali Khamenei has ordered the country's elite Quds Force to step up attacks against the West and its allies around the world.

The Telegraph quoted Western intelligence officials as saying that Khamenei gave the order following a recent emergency meeting of Iran's National Security Council in Tehran.

The meeting discussed a report on the repercussions of the possible overthrow of Syrian President Bashar Assad for Iran.

The report, according to the Telegraph, concluded that Iran's national interests were threatened by a combination of UN sanctions and the West's backing of the Syrian opposition.

As a result, the report recommended that Iran issue a warning to "America, the Zionists, Britain, Turkey, Saudi Arabia, Qatar, and others" over its actions in Syria and the rest of the region.