French PM Dominique de Villepin has expressed disappointment at Iran's decision to disregard a UN deadline for stopping sensitive nuclear work.
Iran insists its nuclear work is for peaceful purposes
"We cannot accept that Iran does not respect commitments it has made in the past," Mr Villepin said after talks with Italian PM Romano Prodi in Rome.
Mr Prodi said France and Italy should co-operate over the "Iranian problem".
The US wants UN sanctions against Iran over its failure to meet a 31 August deadline to stop enriching uranium.
Six world powers are set to meet next week to decide on the way forward.
The UN nuclear agency, the International Atomic Energy Agency (IAEA), said on Thursday that Tehran had recently begun a new round of uranium enrichment.
Iranian President Mahmoud Ahmadinejad has said Iran "will not give up one iota" of its nuclear work.
Iran maintains it has a right to a nuclear programme which, it says, has a purely civilian aspect.
Western powers accuse Iran of trying covertly to develop a nuclear bomb.
Mr de Villepin said the world had to show a united front to persuade Iran to abandon its controversial nuclear work.
"We think it is possible to go forward with dialogue but it is important that the international community show Iran the necessity to change position," he said.
His Italian counterpart, Mr Prodi, said both men agreed Iran was "one of the great challenges to resolve".
Co-operation between the two countries had to extend to the "Iranian problem", he said.
Italy has historically had good ties with Tehran and is still Iran's biggest European trading partner, commanding a strong presence in its energy market.
An IAEA report released on Friday said: "Iran has not suspended its enrichment related activities."
"Iran has not addressed the long outstanding verification issues or provided the necessary transparency to remove uncertainties associated with some of its activities," the report added.
But inspectors have found no "concrete proof" that the nuclear programme "is of a military nature", one official told journalists.
An Iranian official said the report "carries no sign Iran's nuclear programme is not peaceful".
The US ambassador to the UN, John Bolton, described the report as a red flag and said it provided ample evidence of Iranian defiance.
Mr Bolton said the UN Security Council must now be ready to impose sanctions on Tehran, but said no action would be taken until EU talks with Iran next week.
EU foreign policy chief Javier Solana is due to hold face-to-face talks with Iran's chief nuclear negotiator Ali Larijani.
The talks will come a day before a meeting of the five permanent UN Security Council members and Germany on the issue, diplomats say.