Iran's expansion of sensitive nuclear activity breaks United Nations resolutions and increases concerns about whether its nuclear program is entirely peaceful, the European Union said on Thursday, May 23, according to Reuters.

A UN nuclear agency report released on Wednesday showed Iran was expanding nuclear activities, in clear violation of resolutions of both the UN Security Council and of the board of the world body's International Atomic Energy Agency (IAEA), the EU said.

It "further aggravates existing concerns on the exclusively peaceful nature of the Iranian nuclear program", a spokesman for EU foreign policy chief Catherine Ashton said.

Critics say Iran is trying to achieve the capability to make atomic arms. Iran denies this, saying it needs nuclear power for energy generation and medical purposes.

The EU spokesman said Iran had continued to refuse to cooperate with the IAEA in its efforts to resolve outstanding issues, including those pointing to possible military dimensions to the Iranian nuclear program.

"It thereby violates the requirements contained in the IAEA board resolution adopted on 13 September 2012, which calls on Iran to step up cooperation with the IAEA," he said.

Ashton represents six world powers in long-running negotiations with Iran over its nuclear program.

The latest IAEA report said Iran is pressing on with construction of a research reactor that Western experts say could eventually produce plutonium for a nuclear weapon if Tehran decides to make one.

It said Iran had added to its capacity to refine uranium, which can also provide the fissile core of a bomb if enriched to a high level.