As Iran gears up for the next round of international negotiations over its uranium enrichment programme — as-yet unscheduled — Western intelligence agencies are concerned that it is pursuing a dual-track route towards the possession of nuclear weapons.

Work on a heavy-water reactor has raised concerns that it will try to build a bomb using plutonium instead. Meanwhile, the latest International Atomic Energy Agency report on Iran’s nuclear activities, presented this week to the UN, confirmed that Iran’s uranium-enrichment programme continues apace.

More moderate noises coming out of Tehran since the inauguration of the new president, Hassan Rouhani, had raised hopes for a more pragmatic attitude at the next round of talks.

At April’s gathering of representatives from Iran and negotiators from the five permanent members of the United Nations Security Council and Germany (P5+1), however, there was no breakthrough.

One encouraging sign has been Iran’s decision to withdraw its hardline chief negotiator, Saeed Jalili, and move responsibility for the talks from the Supreme National Security Council, under the aegis of Supreme Leader Ali Khamenei, to the foreign ministry.

It is now expected that the main negotiator will be the new Foreign Minister, Javad Zarif, who was educated in the West and is a former ambassador to the UN. Iran has also indicated that it is open to bilateral talks with the United States.

In a recent interview with Associated Press, Ali Akbar Velayati, the Supreme Leader’s foreign policy adviser, said that from now on Iran would use “different language” towards the West, although he insisted that the country was not about to suspend its nuclear activities.

While the change in tone has raised hopes of progress in the next round of talks, Western intelligence services have warned that Iran is busy preparing a second route to nuclear weapons that could yield enough fissile material for a bomb by early 2015, even if it agrees to limit its uranium enrichment.

Most of the attention so far has been on the large enrichment programme, which features thousands of centrifuges, but progress in the construction of the heavy-water reactor in Arak, in the north-west, means that Iran could instead use plutonium to construct a bomb. The reactor is scheduled to become operational in late 2014 and it is estimated that it will be capable of producing, annually, enough plutonium for two bombs.

Iran claims that the purpose of the Arak reactor is to produce medical isotopes but Israeli Prime Minister Benjamin Netanyahu said in an interview last month that “they’re pursuing an alternate route of plutonium… to build a nuclear bomb. They haven’t yet reached it, but they’re getting closer to it. And they have to be stopped.”

The reactor is more vulnerable to an attack than the underground uranium enrichment facilities but any strike that could take place after the reactor becomes operational may cause a massive environmental disaster.