A government spokesman said that would put Iran in a state of “inequity”.
The permanent members of the UN Security Council have been trying to agree on a draft resolution which could include sanctions against Iran.
Iran has been offered a package of incentives in exchange for suspending its enrichment programme.
But Iranian government spokesman Gholamhossein Elham said on Monday: “We are ready to discuss anything in negotiations… (but) we will not accept any preconditions.”
He said all parties should be on an equal standing on entering any negotiations, and that halting enrichment would mean Iran was not in such a position.
Iran insists its nuclear programme is entirely peaceful and is designed to meet its energy needs only, but the US and other Western nations fear Iran may develop nuclear weapons.
‘Humiliating’
The BBC’s Tehran correspondent Frances Harrison says the conflict in Lebanon has made Iran increasingly outspoken against Israel and the US, creating a more radical atmosphere that makes it hard for Iranian leaders to compromise on the nuclear issue.
Our correspondent says there have been ominous hints Iran is not interested in the incentives package offered by the West.
On Friday Iran’s moderate former president Hashemi Rafsanjani – who had always backed a compromise – dismissed the package as “humiliating”.
Diplomats say the last meeting between Iran’s top nuclear negotiator Ali Larijani and the EU’s foreign policy chief Javier Solana was a disaster from the European point of view.
They report Mr Larijani spoke for 45 minutes without mentioning the word “nuclear”, and there was no discussion of the ambiguities Iran complains about in the package.
Policy warning
Iran has warned it will change its nuclear policies if states urging it to suspend nuclear enrichment carry out threats against the country.
Mr Larijani said last week Iran still believed in a negotiated settlement, and did not spell out how Iranian nuclear policy might change.
But our correspondent said it could mean suspending international inspections of nuclear sites or its membership of the nuclear non-proliferation treaty.
Mr Larijani also resisted pressure to respond formally to the incentives package, saying Iran needed until late August to formulate its response.
