(Adds details from letter)

WASHINGTON, Aug 5 (Reuters) - Iran gave no concrete response to an incentives offer by world powers to halt its nuclear program but said in a letter it would give a clear reply as soon as possible, according to extracts obtained by Reuters.

"Iran is ready to provide a 'clear response' to your proposal at the earliest possibility, while simultaneously expecting to receive your 'clear response' to our questions and ambiguities as well," according to an extract of the letter delivered to European Union foreign policy chief Javier Solana on Tuesday in Brussels.

The one-page letter to Solana, who represents the United States, China, Russia, France, Britain and Germany on the Iran nuclear issue, said Tehran had "carefully considered" views put forward by officials from the six countries at a meeting in Geneva last month but certain issues needed to be clarified.

"Such mutual clarification can pave the way for a speedy and transparent negotiating process with bright prospect," said the letter, which has not been officially released.

One Western official who had seen the letter, which was circulated to capitals on Tuesday, said it said "absolutely nothing" and no concrete proposals were made by Tehran.

The official said the letter also failed to provide any real response to the offer made by world powers last month of trade, financial and diplomatic incentives in exchange for a freeze of its uranium enrichment activities.

Washington has insisted that a "clear message" from Iran responding to the incentives was required to avoid additional sanctions.

The West suspects Iran of building a nuclear bomb while Tehran argues its atomic work is for peaceful power generation. (Reporting by Sue Pleming; editing by Randall Mikkelsen)

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