The US State Department emphasised that Iran must keep an October 31 deadline set by the International Atomic Energy Agency (IAEA) to prove that it is not developing nuclear weapons.

IAEA chief Mohamed ElBaradei, on a visit to Tehran, said Thursday he had received assurances of Iran's "readiness" to open up its suspect facilities.

He said Iranian officials had shown a willingness to sign up to an additional protocol under the Non-Proliferation Treaty (NPT) that would allow tougher inspections of Iranian facilities.

State Department deputy spokesman Adam Ereli said the US government had only seen the "reports" of ElBaradei's comments.

"From our point of view, we've made it clear that we expect Iran to sign the additional protocol without delay.

"I would also point out that the IAEA board of governors made it clear in a resolution adopted on September 12 that there are a series of things that Iran needs to do by October 31 beyond -- not connected to -- signing an additional protocol, and that they are looking for Iran to cooperate in meeting this deadline."

The spokesman said Iran had to comply with the IAEA resolution "in its entirety, not one issue or another issue."

The IAEA has warned that if Iran does not meet the October 31 deadline it could refer the matter to the UN Security Council, the only body which can order international sanctions.

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