TEHRAN/BERLIN Iran has accused six major powers of "unreasonable behavior" over its disputed nuclear program, but the European Union said on Tuesday it would stick to a dual approach combining diplomacy with the threat of sanctions.
Tehran's accusation was contained in a letter from its top nuclear negotiator, Saeed Jalili, that was delivered to European Union foreign policy chief Javier Solana on Monday.
"It's a letter that in a way complains about our policy but our policy is clear. It's a double-track approach," Solana told Reuters in Berlin on Tuesday.
Asked whether the letter would make negotiations with Iran more difficult, Solana replied: "It's just a letter."
The United States and other Western powers suspect Tehran is seeking a nuclear bomb under cover of its civilian nuclear program. Iran, the world's fourth-largest oil producer, denies it has any such intentions, saying it only wants to generate electricity.
Jalili's letter, a copy of which was obtained by Reuters, was addressed through Solana to foreign ministers of the six-power group consisting of the United States, Britain, France, China, Russia and Germany.
In Washington, a U.S. official said the six powers planned to hold a conference call later this week to discuss the letter and their possible response, but declined to say exactly when.
In June, the six gave Iran a beefed-up offer of political and economic incentives, including nuclear reactors, in exchange for suspending its uranium enrichment program.
Iran responded at the time with a non-committal letter. The group of six handed the United Nations Security Council a toothless draft resolution on Iran's nuclear program in September after Washington, facing stiff Russian opposition, failed to secure agreement for fresh sanctions.
"In the judgment of the world community, this unreasonable behavior is an indication of the lack of a clear response to the principled questions of the Islamic Republic of Iran," Jalili said in the letter.
Iran has shown no sign of compromise, vowing to resist U.S. "bullying" to force it to abandon its right to develop peaceful nuclear technology. Enrichment is at the heart of the dispute because it can be used either to provide reactor fuel or -- if the uranium is purified to a much higher degree -- to supply the fissile material for a nuclear bomb.
Jalili said "logical behavior" by major powers could pave the ground for constructive talks to remove international concerns over the country's nuclear work.
Solana, representing the six powers, and Jalili last discussed Tehran's nuclear program by telephone in August.
"It is interesting ... to see that in the course of talks ... the other party (the major powers) ... resorts to levers of pressure instead of offering answers to questions and trying to remove ambiguities," Jalili said.
A senior Iranian official said Jalili's letter would also be delivered to the Swiss embassy in Tehran on Tuesday. Switzerland represents U.S. interests in Iran since Washington severed ties with Tehran a year after its 1979 Islamic revolution.
(Additional reporting by Susan Cornwell in Washington; writing by Parisa Hafezi; editing by Mark Trevelyan and Mohammad Zargham)