"The venue for holding the meeting is still not fixed," Mottaki was quoted as saying on the state broadcaster's website.
European Union foreign policy chief Javier Solana has said the October 1 talks will "very likely" be held in Turkey.
The five UN Security Council permanent members — the United States, Russia, China, Britain and France — plus Germany are due to take part in the talks with Iran's top nuclear negotiator Saeed Jalili.
The talks will revolve around Tehran's package of proposals which is aimed at allaying concerns over its controversial nuclear programme.
Mottaki, however, ruled out any direct talks between Iranian and US officials during the meeting, the ILNA news agency said.
"This is not a direct talk between Iran and US, but in any case they are present at the negotiating table and different issues will be discussed" with all the parties, he added.
He also voiced hope negotiations will be based "within the framework of Tehran's package."
Tehran's package does not talk of its nuclear programme but calls for nuclear disarmament globally.
