Khamenei hit a defiant tone, saying "no obstacles can stop Iran's nuclear work," speaking on state television shortly after International Atomic Energy Agency (IAEA) inspectors left Iran after being refused access to nuclear facilities.

He reiterated Iran's long-held stance that its nuclear program was for civilian purposes only, despite Western suspicions that Tehran was trying to develop an atomic weapon.

Eyebrows were further raised Wednesday when IAEA inspectors said there had been no agreement on further nuclear talks with Iran, after arriving back in Vienna following the unsuccessful two-day visit to the country.

"We tried to reach agreement on a way forward to resolve all the outstanding issues ... We approached this trip in a constructive spirit. Unfortunately we could not get agreement," IAEA chief inspector Herman Nackaerts told reporters at Vienna airport.

"We could not get access, we could not finalize the way forward," said Nackaerts.

The team had requested access both during this visit and during a first trip in late January to Parchin, near Tehran, where it believes explosives testing has been carried out.

Iran's nuclear program has caused much consternation in recent months, with fears regional rival Israel was considering a pre-emptive strike to eliminate its rival's nuclear facilities.

The deputy head of Iran's armed forces was quoted on Tuesday as saying Iran would also take pre-emptive action against its enemies if it felt its national interests were endangered.

"Our strategy now is that if we feel our enemies want to endanger Iran's national interests, and want to decide to do that, we will act without waiting for their actions," Mohammad Hejazi told the Fars news agency.

dfm/ng (Reuters, dpa)