"The Islamic republic has prepared and presented a response to the letter of the six countries with a constructive and creative view and a focus on common ground," top nuclear negotiator Saeed Jalili was quoted by state television as saying.
"On this basis, the Islamic republic's response to the letter of the six countries' foreign ministers will be delivered today," he added, in a telephone call with EU foreign policy chief Javier Solana.
Last month Solana, on behalf of the world powers, presented Iran with a letter from six foreign ministers and a package offering Tehran technological incentives and full negotiations if it suspends uranium enrichment.
Jalili did not give further details on the contents of the response and did not say if it would be a simple 'yes or no' answer to the package offered by world powers or something more vague.
He also said that both sides had agreed that talks would be held again by the end of the current Iranian month of Tir, which ends in two weeks, without specifying further.
Solana was quoted as saying that "I am sure that by taking positive steps the atmosphere of talks will be constructive and create hope."
Iran has also put forward its own more all-embracing offer aimed at solving world problems, including the nuclear issue, and has said there is common ground between the two packages.
There has been considerable speculation in recent days that Tehran was softening its tone on the nuclear standoff.
The foreign policy adviser to supreme leader Ayatollah Ali Khamenei, Ali Akbar Velayati, said that it would be in Iran's interest to accept the negotiations.
Foreign Minister Manouchehr Mottaki has also spoken of a "new process" under way in the crisis.
Velayati however on Thursday said his comments had been misinterpreted, insisting that "I talked about accepting negotiations and not accepting the proposed package."
The United States has never ruled out taking military action against Tehran and in recent weeks speculation has mounted that Iran's arch regional enemy Israel was preparing to launch pre-emptive strikes against Iran's atomic sites.
In a sign of the continued tensions, the head of Iran's elite Revolutionary Guards, General Mohammad Ali Jafari, warned: "Any action against Iran will be interpreted as the start of a war.
"Iran's response to any military action will make the aggressors regret their decision."
US media reported that more than 100 Israeli warplanes staged a training exercise with Greece last month to prepare for a possible long-distance strike and as a warning to Tehran.
In an unusual move, the letter from the six world powers — to which the details of the package were attached — was personally signed by US Secretary of State Condoleezza Rice along with her counterparts.
"Formal negotiations can start as soon as Iran's enrichment-related and reprocessing activities are suspended," said the text of the world powers' letter which was addressed to both Mottaki and Jalili.
"We want to be clear that we recognise Iran's rights under the international treaties…
"But with these rights come responsibilities, in particular to restore the confidence of the international community in Iran's nuclear programme," it said.
World powers fear that Iran could use enrichment to make a nuclear weapon. Tehran insists its atomic drive is peaceful and aimed only at producing nuclear power for a growing population whose fossil fuels will eventually run out.
No Iranian official has suggested in recent months that Tehran is ready to give any ground on the key question of enrichment, which Iran must suspend in order to enter the talks offered by the world powers.
