Secretary of State Hillary Clinton said Friday the United States was still trying to determine the extent of Iran's response to a UN-brokered plan on nuclear cooperation with major powers.

"We are working to determine exactly what they are willing to do, whether this was an initial response that is an end response or whether it's the beginning of getting to where we expect them to end up," Clinton told CNN television.

Clinton said the United States was "seeking clarification" on Iran's response a day after the International Atomic Energy Agency said it had received a response from Tehran without giving any details of its contents.

She added that Washington, the IAEA, France and Russia "are all united and showing resolve in responding to the Iranian response."

The IAEA said Thursday that the watchdog's director Mohamed ElBaradei had "received an initial response from the Iranian authorities to his proposal to use Iran's low-enriched uranium for manufacturing fuel for ... the Tehran Research Reactor," without giving further details.

Iranian media said meanwhile Tehran was seeking some changes to the fuel supply proposals, and the country's envoy to the IAEA said he expected to be involved in further negotiations.

Iranian President Mahmoud Ahmadinejad however insisted his government, which has for years been in a tense standoff with the West over its refusal to heed repeated UN Security Council ultimatums to suspend uranium enrichment, was ready to strike a deal.

The hardline leader said the West had previously talked of "halting and suspending everything, but now they are talking about fuel exchange, nuclear cooperation, building nuclear power plants and reactors. They have moved from confrontation to cooperation."

Therefore, "the conditions for nuclear cooperation are ready," he said.

Clinton, speaking to CNN from Pakistan where she has been involved in a whirlwind diplomatic mission to shore-up support for US interests there, said she thought it was "very significant that Russia and France and the UK, Germany, China are all united" in their stand against a nuclear Iran.

"This is all of us saying: we came to this idea, you agreed in principle and we expect to have you follow through," Clinton said, adding that she wanted "the process to play out."