New satellite images reveal that an Iranian nuclear site that has been kept away from the inquiring eyes of UN inspectors is operational and apparently producing materials that could eventually be used to make an atomic bomb.

Fresh photographs of the Arak facility, published late Tuesday by Britain’s Daily Telegraph, indicate that heavy water production has commenced at the site, based on a cloud of vapor seen rising from a building there.

Arak is a heavily guarded facility that contains two main sections: a nuclear reactor and a heavy water production plant. The nuclear reactor has been open to visits from foreign officials, including one that was conducted earlier this month. Work on that reactor is nearly complete, and Iran has said it intends to put it online in 2014. However, the heavy water section of the facility has been off-limits to international inspections for the past 18 months.

Most concerns over Iran’s nuclear program have focused on its ability to enrich uranium toward an atomic weapon, but the production of plutonium could offer Tehran an alternative route to the nuclear club.

Heavy water contains high concentrations of the hydrogen isotope deuterium and is used to produce plutonium, an alternative to uranium for manufacturing atomic weapons.

Western governments and the UN’s International Atomic Energy Agency have been aware for some time of activity at the sprawling site, located  240 kilometers (150 miles) southwest of Tehran, but inspectors have not been granted access to the plant since August 2011. An IAEA report last week, presented to its own board, reported that there was ongoing construction and active heavy water production at Arak.

The Daily Telegraph commissioned the images from a commercial satellite operator, and they were taken on February 9, the paper said.

A recent satellite image of the Arak facility shows a cloud of vapor indicating the production of heavy water (photo credit: Daily Telegraph, screenshot)

A recent satellite image of the Arak facility shows a cloud of vapor indicating the production of heavy water (photo credit: Daily Telegraph, screenshot)

The publication of the images come as delicate talks resume in Kazhakstan with Iran about its nuclear program. Those talks have reportedly focused on the Fordo uranium enrichment complex, hidden beneath mountains near the city of Qom.

The images show a large number of anti-aircraft batteries protecting the Arak site — more than any other known Iranian nuclear facility — the report said. Most of the missiles are on the western side of the complex, facing toward Israel and the direction from which an Israeli airstrike would likely emanate, the report said.

In November, Iran’s nuclear chief, Fereidoun Abbasi, said work at Arak was “progressing without any problem according to the schedule” but with caution, “since the enemy intends to harm this reactor.”

Amos Gilad, a senior Defense Ministry official, said on Wednsday afternoon that Israel had been well aware of the Arak facility for years, and that the new images did not indicate a dramatic change. The breathless new reporting was making it sound “like Iran has the bomb,” he said.

In fact, Iran does not have the bomb, Gilad told Army Radio, but it is working to ensure that it has all the capabilities to attain a bomb the moment it takes a decision to get one.

The West is concerned that the heavy water reactor could produce enough plutonium for a nuclear weapon each year, if the spent fuel is reprocessed. That would be another pathway for bomb-grade material, but Iran is not known to possess a plutonium reprocessing facility.

However, North Korea does have that ability, and the two countries are suspected of maintaining close ties in the nuclear arena. Another recent British report said Iranian officials were present earlier this month when North Korea tested a nuclear device, to the outrage of the international community.

The Associated Press contributed to this report.