The U.N. nuclear watchdog agency said Tuesday it has received new information alleging that Iran may be working on a nuclear weapons program, but a senior official familiar with the reports said Tehran in recent years appears to have sharply curtailed any such activity.

In a separate report, the organization — the International Atomic Energy Agency — said it strongly believes that Syria tried to build a nuclear reactor, a finding that sets the stage for the country's referral to the U.N. Security Council within the next few weeks.

Both restricted reports were issued for the June 6-10 meeting of the 35-nation IAEA board where the agency's probes of Iran and Syria are main agenda items. Both reports were obtained by The Associated Press shortly after their release to board members.

"The agency remains concerned about the possible existence in Iran of past or current undisclosed nuclear related activities ... including activities related to the development of a nuclear payload for a missile," said the IAEA. Overall the report said the agency cannot "conclude that all nuclear material in Iran is in peaceful activities."

Asked to put that finding in context, the senior official, who spoke on condition of anonymity because his information is privileged, said that the most recent intelligence suggests that Iran worked on components of a weapons program as late as 2010. But he told the AP that while intelligence up to 2004 had indicated a concerted effort at developing weapons, the more recent information had pointed only to "bits and pieces" of work that seemed weapons related.

That assessment appeared to be new, in differentiating between the scope of alleged weapons work on the part of Iran years ago and now.

Iran has long refused to cooperate with IAEA experts trying to follow up intelligence received from board members that it conducted covert nuclear weapons-related experiments. The Islamic Republic is under four sets of U.N. Security Council sanctions for refusing to stop uranium enrichment — an activity that can make both nuclear fuel and fissile warhead material.

Syria also has been accused of stonewalling the agency.

The United States has said a site in Syria bombed by Israeli warplanes in 2007 was a nearly completed nuclear reactor, built secretly and with North Korean help, that would have produced plutonium, which also can be used for nuclear weapons.

Damascus has denied that, saying it had no hidden nuclear program. But Syria has refused to allow IAEA inspectors to revisit the site after an initial mission found traces of uranium and other materials that strengthened suspicion that the bombed target was nuclear.

While past agency reports have not ruled out that the destroyed site was a reactor, Tuesday's conclusion essentially says Damascus was not telling the truth in denying nuclear activities. "The agency assesses that the building destroyed ... was a nuclear reactor," said the report.

Separately, the senior official displayed comparative photos showing a strong similarity between the destroyed facility and North Korean-type nuclear reactors.

In recent interviews, three diplomats and a senior U.N. official said such an assessment would be the basis of a Western-sponsored resolution at the IAEA board meeting that condemns Syria's refusal to cooperate with the agency and sends the issue to the U.N. Security Council.

Once formally involved, the council has options ranging from doing nothing to passing its own resolutions demanding compliance with the IAEA, followed by sanctions to enforce such demands — as has been the scenario for Iran.

However, sanctions against Syria appear unlikely.

While Iran continues with its nuclear program, intelligence services have said Syria's covert activities were effectively ended by the Israeli bombing of the Al-Kibar site. Also, forcing the issue would detract attention from Iran, the main focus of nuclear concern, and sideline efforts to end Syria's bloody crackdown on its grass-roots pro-democracy movement.

But diplomats said that beyond sending a signal to Syria that defying the IAEA carries a price tag, reporting it to the Security Council also would be a rehearsal for more action against Iran. They said that after more than four years of gridlock in IAEA attempts to investigate Iran's alleged nuclear weapons-related experiments, IAEA chief Yukiya Amano also is planning to draw up an assessment — perhaps by the end of the year — saying that such experiments were likely conducted.

That, in turn, would open the path for renewed IAEA referral of Iran to the U.N. Security Council and lead to potential tightening of existing sanctions or a new set of U.N. penalties, the diplomats said.

Along with Iran, Syria denies allegations that it is — or was — interested in developing nuclear arms. But its refusal to allow IAEA inspectors new access to the bombed desert site has heightened suspicions that it had something to hide along with its decision to level the structure that was destroyed by Israel and later to build over it.

Drawing on the 2008 visit to Syria by its inspectors, the IAEA determined that the destroyed building's size and structure fit specifications that a reactor would have had. It also found graphite and natural uranium particles that could be linked to nuclear use of the structure.