Iran says it will reject any offer to resolve the dispute over its nuclear programme that forces it to halt its "peaceful activities".
President Mahmoud Ahmadinejad said such an initiative by European countries would be "without any value".
Britain, France and Germany are drawing up proposals aimed at persuading Iran to give up uranium enrichment by offering it a series of incentives.
It says its nuclear programme is aimed at meeting its energy needs only, and insists on its right to enrich uranium.
But on Sunday Mr Ahmadinejad said the Europeans "know that any proposal that requires a halt to our peaceful activities will be without any value".
He said Western powers "behave like masters who still believe they are in the colonial era".
Our correspondent says it is a measure of the West's desperation that it has had to resort to a new offer of incentives.
The chances of getting tougher wording on a UN resolution to threaten Iran appear slim, he adds.
Both China and Russia, which are veto-holding members of the Security Council, do not want to support any move which might open the door to military action.
The United States, Russia, China, Britain and France plus Germany are to meet in London next Friday.
http://news.bbc.co.uk/1/hi/world/middle_east/4768865.stm