VIENNA, April 15 -- The UN nuclear agency wants to speed up the resolution of the Iranian nuclear issue but "it depends very much on the level of cooperation and will of Iran," the UN nuclear agency chief told Xinhua in an interview Tuesday.

Speaking of dealing with the so-called "possible military dimension" of Iran's nuclear program, Yukiya Amano, Director General of the International Atomic Energy Agency (IAEA), said the "pace should be accelerated."

He said the IAEA expects to step forward, together with Iran, to deal with the unclarified issues surrounding Tehran's nuclear plan to ensure the peaceful nature of the program.

But the Japanese veteran diplomat seems to be worried that it could take "a long time" to resolve the 12 areas of issues related to possible military dimensions if the cooperation progresses slowly.

The cooperation framework signed last November stipulated that IAEA and Iran shall start dealing with the activities relating to possible military dimensions in May.

But the head of UN nuclear watchdog told Xinhua that thus far, there has been no proposed timeline nor clear answers from Tehran regarding cooperation.

"They don't say no but they don't say yes," he said, citing the example of Parchin Plant, a suspected military site in which nuclear-related explosive tests are allegedly carried out. IAEA has constantly requested access to Parchin for nuclear inspectors, but have been rejected by Iran.

"It depends very much on the future development," he added.

Western states have long accused Iran of using delaying tactics in the verification of alleged outstanding issues with the country's cooperation with IAEA.

In November 2011, an IAEA report said the agency had gathered "credible evidence" that Iran might carry out experiments and activities relevant to nuclear weapon development, which Tehran denied.

Since Iran's relatively pragmatic President Hassan Rouhani took office last year, Tehran has softened its hardline stance and expressed a will to address the issue of its nuclear program with IAEA.

The country last year reached an accord with six countries, namely Britain, China, France, Germany, Russia and the United States, in Geneva to curb the country's some disputed nuclear activities in exchange for easing some international sanctions.

These changes are seen by Amano as positive, but the agency chief noted that "the basic picture (of Iranian nuclear policy) hasn't changed."

Iran has not implemented the modified code 3.1, which requires member states to provide the IAEA with early notification of planned construction of nuclear facilities; nor has it complied with its additional protocol, which commands greater transparency of its nuclear program, Amano said.

Thus, IAEA could not conclude all the nuclear material and facilities in Iran are for a peaceful purpose, he said.