It will take a lot of work to determine by the end of the year whether Iran was previously developing nuclear weapons, the head of the U.N.'s nuclear watchdog said on Monday.

Alongside the July 14 political agreement with six world powers world powers, Iran reached a roadmap accord with the International Atomic Energy Agency which requires Tehran to pass on enough information about its past nuclear program to allow the U.N. body to report on the issue by December.

"With regard to clarification of PMD, much work needs to be done," Yukiya Amano, IAEA director general, told a news conference, referring to the term "possible military dimensions".

The assessment is a vital part of the deal between Iran and the six powers -- the United States, Britain, France, Germany, Russia and China -- to restrict its nuclear program in exchange for a lifting of international sanctions.

Iran provided the IAEA on Aug. 15 with documents and explanations in writing related to "past and present outstanding issues", Amano told a meeting of his agency's board of governors on Monday, according to the text of his speech.

The agency was reviewing the information and would send questions to Iran on Sept. 15, he said.

"I do not have a particular concern that we will not be able to complete our assessment by the 15th of December," Amano said.

By Rueters