The United States said it would study the response carefully. But it said it would quickly seek UN sanctions if Tehran did not suspend plans for nuclear enrichment as demanded by the Security Council.
The European Union also said the document required careful analysis.
"The document is extensive and therefore requires a detailed and careful analysis," EU foreign police chief Javier Solana.
Iran's nuclear negotiator Ali Larijani delivered the written response to representatives of the five permanent Security Council members plus Germany.
Iran proposes talks
The group drew up the package of incentives for Iran to renounce uranium enrichment and reprocessing activities.
"Iran is ready for serious talks with the 5+1 group from August 23 over the offered package," the student ISNA news agency quoted Mr Larijani telling the envoys.
"We prepared the response to the package with a positive view and even tried to open a way for fair talks by interpreting the many cases of ambiguity logically and positively," he said.
He called on the world powers that backed the offer to "return to negotiations", adding that Iran "is ready to play its role as a responsible country".
But he did not elaborate on what was in the written response, and made no direct reference to an August 31 deadline for Iran to freeze enrichment or risk UN sanctions.
All the indications ahead of Iran's submission were that it was set to reject the basic precondition set by the six powers.
Ayatollah Ali Khammenei, who has the last word on all key policy issues, had said Monday that Iran was determined to press ahead with its nuclear program despite the Security Council deadline.
Atomic Energy Organisation deputy head Mohammad Saeedi said the same day that Iran would "provide Europe with an exceptional chance for an understanding and a return to the negotiating table," but insisted an enrichment freeze was "no longer possible".
Divisions emerge
Divisions were emerging among world powers over how to handle the crisis.
The United States wants sanctions while China said punishing Iran was not the way to resolve the issue.
"We will obviously study the Iranian response carefully," US ambassador to the United Nations John Bolton told reporters in New York.
"But we are also prepared, if it does not meet the terms set to proceed here in the Security Council... with economic sanctions.
"I think we will be prepared to submit elements of a resolution in the Council very quickly," he said.
But a Chinese official said Beijing opposed sanctions.
"We have all along stood for a peaceful settlement of the issue through negotiations, rather than resorting to force or threatening sanctions," said Sun Bigan, special envoy to the Middle East.
"Resorting to force and sanctions cannot fully solve the problems."
The proposal, originally submitted to Tehran in June, offers trade and technology incentives in return for a freeze on enrichment, which can make the fuel for nuclear power stations or in extended form can produce the fissile core of an atom bomb.