"We are looking for progress," US ambassador Gregory Schulte told reporters at the International Atomic Energy Agency (IAEA) headquarters in Vienna.

He said Washington was waiting to see whether Iran had been prepared to give a detailed response to allegations -- backed up by intelligence from a number different sources -- that it had been in involved in weaponisation studies in the past.

The US also wanted to see readiness on Tehran's part to implement the so-called Additional Protocol, part of the Nuclear Non-Proliferation Treaty (NPT) which gives IAEA inspectors the right to carry out unannounced checks at nuclear sites.

"And we're also waiting to see whether Iran is prepared to suspend uranium enrichment," a process used to make the fissile material for an atomic bomb, Schulte said.

The IAEA's last report on Iran back in February contained intelligence showing the Islamic republic had engaged in studies, engineering work and procurement relevant to the design and weaponisation of a nuclear device.

At the time, Iran simply dismissed the allegations as baseless and the intelligence used to back it up as fake.

But the IAEA insisted that such a response was not acceptable and Tehran must present evidence to prove it was not engaged in any such studies.

IAEA inspectors have made a number of visits to Tehran in recent weeks to discuss the issue.

Diplomats close to the IAEA say the agency's latest report could be circulated to governors at the end of this week or early next week so that it can be discussed by the board at a meeting at the beginning of June.

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