Iran and six world powers seeking to coax Tehran into curbing its nuclear activities appear to be coming to talks later this month without resolving the differences that scuttled previous rounds, according to recent letters exchanged between the two sides.

One letter, shared with The Associated Press on Friday, shows Iran seeking an expert-level meeting ahead of the June 18-19 Moscow negotiations to "prepare the necessary ground for the Moscow talks."

In response, a senior European Union representative speaking for the six powers suggests there is no need for such preliminary talks because the six remain committed to their "straightforward proposal" presented at the last meeting in Baghdad.

Her letter instead urges Tehran to embrace that proposal, which offers a mix of incentives if Tehran reduces uranium enrichment, which can generate weapons-grade material as well as nuclear fuel.

On Friday, the U.N. nuclear agency failed to coax Iran into allowing it to reopen a long-dormant probe of suspicions that Tehran worked secretly on atomic arms, further burdening the atmosphere ahead of the Moscow talks.

The International Atomic Energy Agency's investigation has been stalled by Iran's insistence that the allegations are based on forged U.S. and Israeli intelligence. The six powers — the United States, Russia, China, Britain, France and Germany — had been watching the outcome of the agency talks in Vienna closely for signs of Iranian flexibility.

But the day-long meeting broke up without agreement, and IAEA negotiator Herman Nackaerts said Iran came to the table with new conditions instead of signing off on a previous draft. "There has been no progress ... this is disappointing," Nackaerts told reporters, adding that no date for a new meeting had been agreed upon.

Iranian envoy Ali Asghar Soltanieh said "there is no obstacle" to a future deal. But the inconclusive meeting fell far short of expectations raised by IAEA chief Yukiya Amano, who cited the Iranian side late last month as assuring him that agreement was near.

Resumption of the investigation has gained urgency in recent months because of IAEA concerns about a site it suspects was used to test ways of setting off a nuclear charge with high explosives.

The agency late last month showed IAEA board member nations satellite images indicating a cleanup of the site, saying the photos depicted water streaming out of one building, the razing of several other buildings and removal of earth at the facility.

Such activities at the Parchin military base southeast of Tehran are a recent IAEA concern, but Iran's stonewalling of requests of access to sites, scientists and documents the agency says are linked to dozens of suspected cases of secret nuclear weapons work goes back to 2007.

Additional international attention is focused on Iran's uranium enrichment work — particularly its decision last year to start enriching to a level that can be turned quickly into the core of nuclear missiles.

The six powers are seeking to coax Tehran into stopping this activity but the Islamic Republic says it needs to continue higher-grade enrichment to 20 percent to power a research reactor and to make medical isotopes.

Iran denies any interest in nuclear weapons and wants the international community to ease sanctions before it makes a move, something Western nations among the six powers are unwilling to do. Instead, they are offering spare parts for Iran's aging commercial airline fleet and other goods restricted by sanctions.

An Iran armed with nuclear weapons is considered a threat. Israel has indicated readiness to attack Iran if diplomacy and sanctions fail. The U.S. has said it wants to keep "all options" on the table. Both suspect that Iran is aiming to build nuclear weapons, and Israel believes it would be a prime target.

But the letters show little progress in bridging differences less than two weeks before the Moscow talks and before sanctions are tightened still further on Iran's oil. The U.S already has started to enforce penalties against countries importing Iranian crude, and the 27-nation European Union, which recently accounted for 18 percent of Iran's oil shipments, plans to begin an oil boycott July 1.

Dated Monday, the Iranian letter is signed by Ali Bagheri, his country's No. 2 nuclear negotiator. It complains of a lack "of any oral or written response" to Tehran's request for a preliminary meeting ahead of the Moscow talks.

But senior EU official Helga Schmid suggests in a letter dated Thursday that the six-power proposal at the Baghdad talks stands and addresses "our key concerns on the 20 percent enrichment activities" while offering "interesting opportunities for cooperation in the nuclear and other areas."

Comments posted Friday by Iranian President Mahmoud Ahmadinejad on his website also suggested a tough line by Tehran ahead of the Moscow talks.

"If Iran wants to build an atomic bomb, it doesn't fear anyone and will publicly announce it and no one will be able to prevent it," Ahmadinejad said, while insisting the Iran has no intention of building nuclear weapons.


Associated Press writer Ali Akbar Dareini contributed from Tehran.