The International Atomic Energy Agency (IAEA), the UN's atomic watchdog policing restrictions placed on Iran's nuclear activities, told member states on Tuesday it has "verified that 11 metric tonnes of nuclear-grade heavy water have arrived at its destination."

"On 6 December the agency verified the quantity of 11 metric tonnes of the nuclear-grade heavy water at its destination outside Iran," a diplomat quoted the five-paragraph IAEA report as saying.

"This transfer of heavy water out of Iran brings Iran's stock of heavy water to below 130 tonnes," the level set out by the nuclear accords.

While not in it itself radioactive, heavy water can be used as a moderator in nuclear power stations. Plutonium used in nuclear weapons can be extracted from the spent fuel of such reactors.

Last month, the watchdog told members that Iran's heavy water stock had exceeded the 130-tonne mark set out in the nuclear accord by 100 kilograms. Iran's nuclear authority then said that it would ship out 11 tonnes to Oman.

A diplomatic source told news agency dpa that IAEA inspectors were on location to check the arrival of the material, although they could not confirm the location.

Trump and sanctions: US-Iran relations remain strained

Last year, Iran closed a landmark deal with the United States, Britain, France, Germany, Russia and China, preventing Tehran from producing nuclear weapons. In exchange, the international community agreed to lift sanctions on the Islamic Republic.

However, the accord has often come under strain. While Iran's latest move to ship out excess heavy water signals a step in the right direction, it may not be enough to salvage the landmark nuclear deal.

U.S. President-elect Donald Trump had originally vowed during his campaign to scrap the deal, describing it as "the worst deal ever negotiated." He has since softened his tone, but warned that he would "police that contract so tough [the Iranians] don't have a chance."

Last week, the US Senate voted 99-1 to extend the Iran Sanctions Act for a further 10 years. US lawmakers said renewal of the sanction bill was necessary to allow the president to "snap-back" sanctions should Iran break its nuclear commitments.

The law allows the US to sanction businesses for doing business with Iran.

Rouhani speaks out against Sanctions Act

Iran's President, Hassan Rouhani, hit back at the US on Tuesday, saying that he would not allow Trump to "tear up" the nuclear deal. He also warned that Tehran would react to any extension of American sanctions.

"The U.S. is our enemy," Rouhani said. "They want to put as much pressure on us as they can."

Rouhani was speaking at a University of Tehran event commemorating the Iranian students killed by US-backed security forces for protesting a visit by then U.S. Vice President Richard Nixon in 1953.

Obama is expected to sign the Iran Sanctions Act into law, said a White House official, adding that the administration does not believe it violates the nuclear deal.

However, Rouhani said that keeping sanctions on the books, even if they remain suspended, amounts to a breaching of the agreement. "If this is implemented... it would be a blatant and clear breach of the [nuclear agreement] and would face a very harsh reaction from us," he said.

dm/bw (dpa, AP, Reuters)