Nevertheless, Tehran was continuing to refuse to answer any questions on the issue, effectively blocking a long-running investigation into the matter, Yuikya Amano, head of the International Atomic Energy Agency (IAEA), said.

In its latest report on Iran's controversial nuclear drive, the IAEA recently revealed that it had received new information about possible military dimensions to Tehran's atomic activities.

The agency has been investigating Iran's nuclear programme for eight years now, but has so far been unable to establish whether it is entirely peaceful as Iran claims or masks a covert drive to build a bomb as western powers believe.

The 12-page report, circulated to IAEA member states at the end of last month, did not elaborate further about the nature of the new information.

But Amano was quizzed about it at a news conference on the first day of the traditional spring meeting of the IAEA's 35-member board of governors here.

And he said the data appeared to suggest that the weaponisation work may have gone on more recently than previously thought.

"Unfortunately, I cannot say a lot on this issue. But I can tell you that we have received information" between the last board meeting in December and now, Amano said.

"In general terms, we have been collecting information from various sources at various times. Since the previous board in December, we have received some information raising further concerns."

When asked whether the information concerned possible weaponisation work beyond 2004, Amano replied: "I cannot specifically say up to when. But we can say there is some information that indicate the existence of activities beyond 2004."

The Japanese diplomat insisted the IAEA was not saying that Iran still had an active nuclear weapons programme.

"We have concerns and we want to clarify the matter," he said.

But Iran was refusing to answer any questions about the allegations, Amano complained.

"We would like to interact with Iran on the clarification of the issues with possible miliary dimensions," he said.

"Unfortunately, since I came into office, Iran has not engaged with us in the clarification of issues that might have military dimensions. Therefore there has not been progress."

Among the many unresolved issues about Iran's atomic drive are allegations that Iran was involved in weaponisation studies -- work which included uranium conversion, high explosives testing and the adaptation of a ballistic missile cone to carry a nuclear warhead.

Iran has dismissed the evidence as "fabricated" and refused to discuss the so-called "alleged studies" any further.