By Fredrik Dahl

VIENNA (Reuters) - China and Russia are expected to join four Western powers in voicing deep concern about Iran's atomic activities this week and pressing it to cooperate with a stalled inquiry by the U.N. nuclear agency, diplomats said on Tuesday.

A draft statement by the six powers, expected to be delivered during a June 3-7 meeting of the 35-nation board of the International Atomic Energy Agency, says it is essential and urgent for Iran to engage with the IAEA.

The statement - which diplomats said had yet to be formally approved by all six governments - appeared intended to signal continued big power unity in the decade-old dispute over Iran's nuclear program.

The West suspects Iran is seeking the capability to make nuclear weapons. Iran denies this.

Western diplomats made clear they would have preferred the text to be more strongly worded but that this was not possible if they wanted Moscow and Beijing - which have criticized unilateral Western sanctions against Tehran - on board.

They spoke a day after IAEA chief Yukiya Amano, in unusually blunt criticism, told the quarterly board meeting that the agency's talks with Iran had been "going around in circles" for some time.

The IAEA has been trying since early 2012 to engage with Iran over what the Vienna-based U.N. agency calls the "possible military dimensions" to its nuclear program.

But 10 rounds of negotiations in the last 17 months have failed to achieve any breakthrough. Western diplomats accuse Iran of stonewalling the IAEA's investigation into suspected atomic bomb research by Tehran, an allegation it rejects.

POWERS "DEEPLY CONCERNED" - DRAFT

The powers' draft statement expresses concern that no agreement has yet been reached on unblocking the IAEA's investigation, diplomats said. It calls on Iran to grant access to its Parchin military facility, where the IAEA believes the Islamic state may have carried out explosives tests relevant for nuclear weapons development, possibly a decade ago.

Iran says Parchin is a conventional military facility and denies Western allegations that it is now cleaning the site of any traces of illicit atomic activity there.

The IAEA board was meeting in Vienna at a time of apparent deadlock in a broader diplomatic push by the six powers - the United States, Russia, China, France, Germany and Britain - to find a peaceful solution to the row over Iran's nuclear aims.

Western diplomats say they are awaiting the outcome of Iran's June 14 presidential election but still do not anticipate any notable rollback from its nuclear defiance.

Iran, a big oil producer now under Western sanctions, says its nuclear program aims to meet the electricity needs of a rapidly growing population and advance scientific research.

But its refusal to suspend nuclear activity with both civilian and potential military applications in defiance of U.N. Security Council demands, and its lack of full openness with the IAEA, have fuelled suspicions abroad about its ultimate goals.

Israel, widely assumed to be the Middle East's only nuclear-armed state, sees Iran's declared civil nuclear program as the most serious risk to its security and has threatened air strikes if diplomacy and sanctions fail to rein in Tehran.

In their draft, the six powers said they were "deeply concerned" about Iranian nuclear activities in defiance of U.N. Security Council demands to suspend them, including uranium enrichment and the construction of a reactor, diplomats said.

(Editing by Angus MacSwan)