The United Nations' nuclear watchdog, the International Atomic Energy Agency (IAEA), on Monday expressed concern over the lack of up-to-date information about Iran's heavy water reactor that is currently under construction.

"The lack of up-to-date design information on the IR-40 reactor is having an increasingly adverse impact on our ability to effectively verify the design of the facility," IAEA chief Yukiya Amano told a meeting of the UN agency's 35-nation board of governors, adding Iran should fully cooperate to clarify the "outstanding issues" over its disputed nuclear program.

IAEA's latest report showed Iran had yet to offer design details on its 40 megawatt heavy water reactor under construction in Arak.

The west is increasingly concerned the reactor could be used to produce weapons-grade plutonium and potentially produce a nuclear bomb. However, Iran has repeatedly stated its nuclear program is peaceful and aimed at power generation, research and development.

IAEA has accused Iran of failing to comply with existing agreements, according to which Iran should offer the design information of its nuclear facilities. Both parties will meet for an 11th round of talks on September 27 in Vienna, aimed at striking a deal on a "structured approach" toward a nuclear inspection framework.

Previous talks over the past two years over the issue have yielded no substantial progress.

Western states have been long accusing Iran of developing nuclear weapon under cover of civilian nuclear program, but Iran says the suspicion is baseless and fabricated.