A drawing based on information from inside an Iranian military site shows an explosives containment chamber of the type needed for nuclear arms-related tests that UN inspectors suspect Tehran has conducted there.

Iran denies such testing and has neither confirmed nor denied the existence of such a chamber.

The computer-generated drawing was provided to The Associated Press by an official of a country tracking Iran's nuclear program who said it proves the structure exists, despite Tehran's refusal to acknowledge it.

A satellite image provided by DigitalGlobe and the Institute for Science and International Security shows the military complex at Parchin, Iran, 30 kilometres southeast of Tehran. (DigitalGlobe/Institute for Science and International Security)The image is based on information from a person who had seen the chamber at the Parchin military site, the official said, adding that going into detail would endanger the life of that informant. The official comes from an IAEA member country that has been severely critical of Iran's assertions that its nuclear activities are peaceful and asserts they are a springboard for making atomic arms.

A former senior IAEA official said he believes the drawing is accurate. Olli Heinonen, until last year the UN nuclear agency's deputy director general in charge of the Iran file, said it was "very similar" to a photo he recently saw that he believes to be the pressure chamber the IAEA suspects is at Parchin. He said even the colours of the computer-generated drawing matched that of the photo he had but declined to go into the origins of the photo to protect his source.

Meeting in Vienna

After months of being rebuffed, IAEA and Iranian officials meet starting Monday in Vienna, and the IAEA will renew its attempt to gain access to the chamber, allegedly hidden in a building. Any evidence that Iran is hiding such an explosives containment tank, and details on how it functions, is significant for IAEA investigations.

Beyond IAEA hopes of progress, the two-day meeting is being closely watched by six powers trying to persuade Iran to make nuclear concessions aimed at reducing fears that it may want to develop atomic arms as a mood-setter for May 23 talks between the six and Tehran in Baghdad.

Warnings by Israel that it might attack Iran's nuclear facilities eased after Iran and the six - the United States, Russia, China, Britain, France and Germany - met last month and agreed there was enough common will for the Baghdad round. But with the Jewish state saying it is determined to stop Iran before it develops the capacity to build nuclear weapons, failure at the Iraq talks could turn such threats into reality.

In Tehran on Sunday, Saeed Jalili, Iran's top nuclear negotiator, said it was up to the Western nations coming to the Baghdad talks to "build trust of the Iranian nation," adding, "Any kind of miscalculation by the West will block success of the talks."

The IAEA has been stonewalled by Iran for more than four years in attempts to probe what it says is intelligence from member states strongly suggesting that Iran secretly worked on developing nuclear weapons.

Satellite images

It mentioned the suspected existence of the chamber for the first time in a November report that described "a large explosives containment vessel" for experiments on triggering a nuclear explosion, adding that it had satellite images "consistent with this information."

It did not detail what the images showed, but a senior diplomat familiar with the IAEA's investigation who has also seen the image provided to the AP said they revealed a cylinder similar to the image at Parchin. Subsequent photos showed a roof and walls going up around the cylinder that hid the chamber from satellite surveillance.

IAEA chief Yukiya Amano said in March his agency has "credible information that indicates that Iran engaged in activities relevant to the development of nuclear explosive devices" at the site. Diplomats subsequently told the AP the experiments also appear to have involved a small prototype neutron device used to spark a nuclear explosion — equipment that would be tested only if a country was trying to develop atomic weapons.

Iran has strenuously denied conducting such work — and any intentions to build nuclear weapons— but has been less clear on whether the structure where it allegedly took place exists.

Attempts to get Iranian comment were unsuccessful. A copy of the diagram was attached to an email sent to Ali Asghar Soltanieh, Iran's chief delegate to the IAEA, with a note that the AP would be asking for reaction. Subsequent phone calls over the weekend went to his voice mail.