Six world powers have agreed to express their "deep concern" about Iran's nuclear programme in a show of unity at a meeting of the UN atomic agency, diplomats said Tuesday.
The US, China, Russia, Britain, France and Germany are "deeply concerned that Iran continues to undertake certain nuclear activities" in contravention of UN Security Council resolutions, according to a draft seen by AFP.
The statement from the five permanent members of the UN Security Council and Germany was due to be given at a closed-door meeting of the International Atomic Energy Agency's 35-nation board of governors in Vienna on Wednesday.
They also say it is "essential and urgent" for Iran to engage with the IAEA over alleged efforts towards developing nuclear weapons, mostly before 2003 but possibly ongoing.
Ten meetings between the IAEA and Iran since the release of a major November 2011 report by the agency on these allegations have been fruitless.
IAEA head Yukiya Amano said on Monday that the two sides were "going around in circles".
Iran denies pursuing the bomb and says that UN Security Council resolutions calling for a suspension of the most sensitive parts of its nuclear programme are illegal.
Tehran maintains the activities are for energy purposes and for medical isotopes.
The IAEA's latest quarterly report on Iran, circulated on May 22, showed it continuing to build up its capacity to enrich uranium, which in highly purified form could be used in a nuclear weapon.
The IAEA report also detailed advances by Iran building a new reactor at Arak which could provide Tehran with plutonium -- an alternative to uranium for a bomb -- if the reactor fuel is reprocessed.
The six powers, known as the E3+3 or the P5+1, are also involved in diplomatic efforts parallel to those of the IAEA.
The last round in April in Kazakhstan "enhanced mutual understanding of the concerns of both sides" but the two sides "remained far apart on the substance," according to the new statement.
It said they wanted a "positive response from Iran to their package proposal, for an initial confidence-building step, which could serve as a good basis to narrow down differences through further dialogue."