VIENNA — China and Russia joined four Western powers in pressing Iran on Wednesday to cooperate with a stalled investigation by the U.N. nuclear agency into suspected nuclear research by the Islamic state.

In a joint statement intended to signal their unity in the decade-old dispute over Iran's nuclear program, the six powers said they were "deeply concerned" about the country's atomic activities. Iran denies having any nuclear weapons agenda.

But, like previous such diplomatic initiatives, it looked unlikely to have any immediate impact in softening Iran's defiance in the face of increasing international pressure to make it curb activity with both civilian and military uses.

The West suspects Iran is seeking the capability to develop nuclear weapons behind the facade of an atomic energy program.

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 airstrikes if diplomacy and sanctions fail to rein in Tehran.

Western envoys said they would have wanted the powers' statement to be more strongly worded but this was not possible if they wanted Moscow and Beijing — which have said Western sanctions against Tehran are counterproductive — to agree to it.

"We are deeply concerned that Iran continues to undertake certain nuclear activities contrary" to U.N. Security Council and [International Atmic Energy Agency] IAEA board resolutions," the powers said in the text read out by Germany's ambassador at a meeting of the 35-nation governing board of the U.N. nuclear agency in Vienna.

These included steps to install more advanced uranium enrichment centrifuges, and the construction of a research reactor, said the statement, which Reuters first reported about on Tuesday.

The IAEA has held 10 rounds of negotiations with Iran since early 2012 in a so-far fruitless effort to get it to address indications of what the Vienna-based U.N. agency calls the "possible military dimensions" to its nuclear program.

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 dispute.

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, says its nuclear program aims to meet the electricity needs of a rapidly growing population and advance scientific research.