(Reuters) - Iran questioned world powers´ readiness for negotiations over its disputed nuclear program and accused the U.N. watchdog on Wednesday of behaving like a Western-manipulated intelligence agency, keeping up its sparring ahead of talks in Moscow.

Iranian media said Tehran had written twice to Britain, France, Russia, China, the United States and Germany - otherwise known as the P5+1 - seeking preparatory meetings before the talks due on June 18, but had yet to hear back.

"The other side´s delay in meeting deputies and experts throws doubt and ambiguity on their readiness for successful talks," Iran´s chief negotiator Saeed Jalili said in a letter to EU foreign policy chief Catherine Ashton, according to the IRNA news agency. Ashton is handling contacts with Iran on behalf of the six powers.

Iranian President Mahmoud Ahmadinejad said the Western powers were seeking to "waste time" and "looking for excuses" by refusing to engage in preparatory talks with Iran.

Under the persistent threat of military strikes by Israel and ever tighter economic sanctions from the West, Iran has returned to nuclear talks that had stalled in early 2011.

Diplomats say Iranian negotiators were more forthcoming at talks in Baghdad last month than in previous negotiations, and believe Supreme Leader Ayatollah Ali Khamenei, Iran´s highest authority, has given them a freer hand to explore a deal.

"Of course, the Islamic Republic does not expect the nuclear issue to be resolved in one meeting," IRNA quoted Ahmadinejad as saying on the sidelines of a summit in Beijing.

At the heart of the decade-long standoff is Iran´s insistence on the right to enrich uranium and that sanctions should be lifted before it shelves activities that could lead to its achieving the capability to develop nuclear weapons.

Western powers insist Tehran must first shut down higher-grade enrichment - beyond that needed for power stations - before sanctions could be eased on the major oil producer.

Diplomats say Iran may offer the U.N. International Atomic Energy Agency increased cooperation in separate talks on Friday as a bargaining chip in the discussions with world powers.

But Iran´s IAEA Ambassador Ali Asghar Soltanieh showed little appetite for making concessions, telling reporters in Vienna: "Unfortunately the agency, which is supposed to be an international technical organization, is somehow playing the role of an intelligence agency."

Full transparency and cooperation with the IAEA is one of the elements the world powers are seeking from Iran, which denies Western accusations that it is seeking to develop the means and technologies needed for building atomic bombs.

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The U.N. agency aims to seal a framework agreement that would unblock its investigation into suspected nuclear bomb research. It wants to visit a military site, Parchin, where it suspects Iran has carried out explosives tests that could be used to develop nuclear arms.

Iran, which says Parchin is a conventional military site, has so far denied access.

Western diplomats said Soltanieh´s harsh remarks aimed at the IAEA cast further doubt on the chances of a successful outcome in the June 8 talks between Iran and the U.N. nuclear agency.

Robert Wood, the acting U.S. envoy to the IAEA, told reporters the attack on the agency was "extremely unfortunate" and he said he was "not optimistic" that there would be a deal signed on Friday.

"Iran needs to stop trying to undermine the integrity of the agency and its work and cooperate with the agency to answer all the outstanding questions with regard to its nuclear program," Wood told reporters.

A European diplomat described Soltanieh´s statement as "confrontational" and said it sent a negative signal to this week´s talks in Vienna that Iran would not compromise at all.

Iran is showing no willingness "to engage on issues of substance" with the IAEA, the diplomat said.

It was unclear what Iran aimed to gain from its proposed preparatory talks before meeting world powers.

Western diplomats often have accused Tehran of seeking to buy time for its nuclear activities by trying to engage in talks about process rather than substance, without real intention of making any concrete concessions.

An adviser to Iran´s supreme leader was quoted as saying on Tuesday that the talks could have a positive outcome if the world recognized Iran´s "inalienable nuclear rights". Tehran says that as a member of the nuclear Non-Proliferation Treaty it can develop a full nuclear fuel cycle.

Washington said on Tuesday Iran had to move first to make its nuclear work compatible with international law and demanded it let U.N. inspectors into the military site that the West believes has been used for weapons-related nuclear research.

A spokeswoman for the EU´s Ashton said on Wednesday she would contact Jalili before the planned Moscow negotiations but saw no need for further preparatory meetings.

"We have made it very clear that preparatory work is ongoing and political issues need to be dealt with on political level," she said.

(Additional reporting by Andrew Quinn in Washington, Justyna Pawlak in Brussels; Writing by Alison Williams; Editing by Michael Roddy) (© Thomson Reuters 2012. 06/06/12)