"The agency has come to the conclusion that it is very likely that the building destroyed at the Dair Alzour site was a nuclear reactor, which should have been declared to the agency," Yukiya Amano, director-general of the International Atomic Agency, told the agency's board of governors Monday.
He also raised concern over Iran's nuclear program and its "possible military dimensions."
Amano said the Syrian government has failed to cooperate on investigations of the site.
Referring to the Israeli air raid that targeted the site, Amano said: "It is deeply regrettable that the facility was destroyed -- allegedly by Israel -- without the agency having been given an opportunity to perform its verification role. Rather than force being used, the case should have been reported to the IAEA."
In October 2007 the Israeli military confirmed the attack but censored details of the strike.
Amano also indicated "possible military dimensions to Iran's nuclear program," saying the Agency had received information "related to possible past or current undisclosed nuclear-related activities."