Iran has not been forthcoming about its nuclear program and may have failed to declare some facilities to the UN, International Atomic Energy Agency chief Yukiya Amano said in an interview with CNN on Wednesday."Iran is not telling us everything. That is my impression. We are asking Iran to engage with us proactively, and Iran has a case to answer," Amano stated.That includes Iran's refusal, during talks in Tehran this year, to grant UN inspectors access to a military site where they say research work relevant for nuclear weapons might have taken place. Western diplomats say they now suspect Iran may be trying to clean up the Parchin site, southeast of Tehran.But diplomats said Russia and China - which are less keen on tightening sanctions - saw no need for a new resolution so soon after one was passed at the last 35-nation board meeting of the International Atomic Energy Agency (IAEA) in November.Instead, the focus is now on crafting a joint statement to be delivered at the current board meeting, which took the unusual step to adjourn until Thursday to give more time for big power envoys to consult with each other and their capitals.One senior Western diplomat played down any suggestion of major differences between the four Western states - the United States, France, Britain and Germany - and Russia and China.It was "nothing that we can't resolve," the envoy said.A joint statement would underline the importance of the powers' upcoming talks with Iran and also urge it to cooperate with IAEA inspectors after two recent rounds of largely fruitless meetings in Tehran, another Western diplomat said.The Western camp would want to see relatively tough language on Iran to pressure it to cooperate with the IAEA while China and Russia seek a milder statement to help foster a constructive atmosphere for more talks, analysts say.EU foreign policy chief Catherine Ashton, who would lead future talks with Iran on behalf of the six powers, announced on Tuesday there would be an attempt to revive the talks - stalled for more than a year - aimed at allaying suspicions that Iran is developing nuclear weapons.A date and venue have yet to be agreed for the talks, proposed by Iran after a year's diplomatic standstill that has increased fears of a slide into a new Middle East war.Amano said that the IAEA has safeguarded a number of Iranian nuclear facilities which the Islamic Republic has declared to the agency."For these facilities and activities, I can tell that they are in peaceful purpose," Amano said. "But there are also, there may be other facilities which are not declared, and we have the indication or information that Iran has engaged in activities relevant to the development of nuclear explosive devices," he stated.Amano's comments came as six world powers that are poised to restart stalled talks with Iran sought on Wednesday to agree to a unified stance on the Islamic Republic's nuclear program, diplomats at the United Nations' nuclear agency said.The United States and its Western allies - which have led international pressure on Tehran - initially pursued a resolution by the UN agency's board of governors to rebuke Iran over what they see as its failure to answer mounting concerns of a disguised bid to develop nuclear arms capability.