Washington, Dec 29 (IANS): Iran has taken a step forward to implement the nuclear deal with world powers by transferring most of its enriched uranium to Russia, in exchange for lifting most international sanctions imposed on Tehran over its nuclear programme.

A ship carrying over 25,000 pounds (11,000 kg) low-enriched uranium materials departed from Iran for Russia, US Secretary of State John Kerry said, calling it "one of the most significant steps Iran has taken toward fulfilling its commitments".

The shipment included the removal of all of Iran's nuclear material enriched to 20 percent that was not already in the form of fabricated fuel plates for the Tehran Research Reactor, he added.

"I am pleased to report that we have seen important indications of significant progress toward Iran completing its key nuclear commitments under the deal," Kerry said in a statement.

On July 14, the historic nuclear deal was signed in the Austrian capital of Vienna by Iran and the P5 1 group, namely Britain, China, France, Russia, the US, plus Germany.

Under the nuclear deal, Iran promised to significantly scale back its atomic plan to address Western countries' concerns over its alleged nuclear weapon programme.

Besides, commitments of improving transparency of nuclear plan, reducing storage of low-enriched uranium to 300 kg and cutting the output of plutonium, another pathway to nuclear weapons, were made by Iran in exchange for international and Western sanctions relief.

On October 18, Iran and the six world powers announced they started implementing the Vienna agreement, which was titled "Joint Comprehensive Plan of Action".

Kerry said Monday's shipment more than tripled the previous "breakout time" of two-to-three months needed by Iran to acquire enough nuclear material to make an atomic bomb, and "ensures an eventual breakout time of at least one year by Implementation Day."

Implementation Day, which is expected sometime next month, refers to the date when Iran has completed all of its nuclear commitments under the verification of the Vienna-based International Atomic Energy Agency, in exchange for the US, EU and UN sanctions relief.

In the statement, Kerry commended Russia for playing "an essential role" in making the shipment possible by taking materials out of Iran and providing natural uranium in exchange, adding that Kazakhstan, Azerbaijan and Norway also contributed to the effort.

The US will remain vigilant to ensure that the implementation of the nuclear deal "achieves exactly what we set out to do from the very beginning of these negotiations, to ensure that Iran's nuclear programme is and always remains exclusively for peaceful purposes," Kerry said.

Ali Salehi, who heads Iran's atomic energy organisation, has confirmed that Iran had sent 8.5 tonnes of low-enriched nuclear material to Russia and received "around 140 tonnes of natural uranium in return."

However, Iran still possesses more than 200 kg of uranium enriched near 20 percent, much higher than the low-enriched stockpile shipped to Russia with just a technical step away from weapon-grade material.

According to the nuclear deal, Iran is committed to either export the near-20 percent enriched uranium, process it into low-enriched one, or turn it into fuel plates to power a research reactor.