"Even the proposal to suspend enrichment, which we regard as illogical, can be discussed in negotiations," Mr Mottaki told a press conference.
The five UN Security Council members plus Germany expect Iran’s response on August 22 to a package of incentives in return for suspending uranium enrichment work.
Earlier Iran's President Mahmoud Ahmadinejad said that his nation refused to be cowed by the "language of force" in the nuclear standoff.
A defiant President Ahmadinejad rejected a UN Security Council resolution that demands Iran halt the sensitive nuclear work, and called for a Middle East free from the presence of the United States and Israel.
"If they think they can use a resolution as a stick against us, they should know that Iranian people do not bend to language of force," President Ahmadinejad said in a televised speech to a vast crowd in the northwest province of Ardebil.
The UN Security Council on July 31 adopted a resolution requiring Iran to suspend all activities related to uranium enrichment by August 31 or risk possible sanctions.
The West, led by the United States, suspects it could be trying to build nuclear weapons, charges denied by Tehran which says its atomic program is for peaceful purposes.
Call to Annan
President Ahmadinejad said he had spoken to UN Secretary General Kofi Annan by telephone and "told him that we are willing to resolve the problem through negotiations... but by this resolution, we have lost our confidence in them."
He reiterated that Iran would respond on August 22 to the international package of incentives to suspend uranium enrichment that was offered by the five permanent members of the Security Council plus Germany.
"We will give our response on the announced date, and our reply will be based on defending the absolute rights of the Iranian people," he said, amid chants of "nuclear energy is our undeniable right".