"An exact date hasn't been fixed," said a Foreign Office spokesman in London -- which currently holds the EU's rotating presidency -- adding the parties were following only a general guideline of late July or early August.

An Iranian nuclear negotiator, Ali Agha Mohammadi, told AFP that Britain, France and Germany must present their offer for a deal by Monday, which he said was the originally scheduled time, and not a later proposed date of August 7.

The negotiator complained that the August 1 date had been fixed at a previous meeting in London and if the Europeans did not stick to this then Iran would take "measures in line with its national interest".

Mohammadi also expressed scepticism over the content of the proposals, which aim to forge a deal that would give Iran nuclear energy cooperation in exchange for providing guarantees that its controversial nuclear programme is peaceful.

Britain, France and Germany represent the European Union in the delicate negotiations with Iran over its nuclear program.

The EU had said on Tuesday the package would probably be presented in the first week of the month, after hardliner Mahmood Ahmadinejad takes over the presidency on August 3.

Asked whether the European Union would submit the offer on Monday, the Foreign Office spokesman replied: "I very much doubt it, but I can't confirm the dates."