"We are deeply concerned that Iran continues to undertake certain nuclear activities contrary to UN Security Council and IAEA board resolutions," the statement said.

IAEA Director General Yukiya Amano said Monday that Iran had not provided the agency with sufficient information to substantiate its claim that its nuclear program is peaceful. An Iranian official in Moscow later called the allegation “unfounded.”

According to an IAEA report published on February 21, 2013, Iran has installed 12,669 centrifuges to enrich uranium at its biggest nuclear enrichment plant in Natanz as of February 19, 2013, up 2,255 since the previous report. In addition, 180 advanced centrifuges were also installed in the reported period, but are not yet operational. The number of centrifuges at another facility, Fordow, has remained constant since February last year, at 696.

The Institute for Science and International Security (ISIS), a nonprofit organization reporting on nuclear security issues, said 13,555 centrifuges were installed in Natanz as of May 15, up 886 since February.

The United Nations Security Council adopted six resolutions as part of international efforts to address Iran’s nuclear program between 2006 and 2010.

The IAEA believes that a large explosives containment vessel was built at the Parchin site southeast of Tehran in 2000, and that it might be used to conduct experiments related to a nuclear weapons program. These activities are “strong indicators of possible nuclear weapon development,” the agency said. Iran maintains that the base in Parchin is a defense object and is therefore of no interest to the IAEA.