The UN atomic watchdog said Monday it had information that Iran may have been engaged in weaponisation studies more recently than previously thought, AFP reported.
Nevertheless, Tehran was continuing to refuse to answer any questions on the issue, effectively blocking a long-running investigation into the matter, the watchdog's chief Yuikya Amano said.
In its latest report on Iran's controversial nuclear drive, the International Atomic Energy Agency recently revealed that it had received new information about possible military dimensions to Tehran's atomic activities.
The IAEA has been investigating Iran's nuclear programme for eight years, 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.
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" since the last board meeting in December, 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 military dimensions. But unfortunately Iran has not engaged with us recently. Therefore, we could not interact with Iran on these issues," 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 the Islamic republic 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.
The other main issue on the agenda of the closed-door meeting, which was scheduled to last all week, were allegations that Syria had been building an undeclared nuclear reactor at a remote desert site called Dair Alzour until it was destroyed by Israeli planes in September 2007.
Syria granted UN inspectors one-off access to the site in June 2008 but no follow-up visits to either Dair Alzour or other possible related sites since then.
In a sign of his growing impatience with Damascus, Amano sent a letter to Syria's foreign ministry on November 18 asking the government to provide the IAEA with prompt access to relevant information and locations" connected to Dair Alzour.
In response, Damascus has agreed to a new visit by IAEA inspectors, not of Dair Alzour, however, but of a less significant site at Homs in the west of the country, which is not one of the sites viewed as suspect by inspectors.
The visit will take place on April 1.
Amano told reporters that the visit "does not solve all the problems, of course."
But, depending on what inspectors found at Homs, "this could be a step forward in my view," Amano said.