The IAEA's Mohammed ElBaradei had talks in Tehran last week
The foreign ministers of Britain, France and Germany are set to pay an unprecedented joint visit to Iran on Monday to discuss Tehran's controversial nuclear programme.
British officials say the UK has been discussing with the French and Germans the importance of "making clear to Iran the urgent need to address the widespread international concern over its nuclear programme".
The meeting in Tehran scheduled for Tuesday follows negotiations in the past week between Tehran and the International Atomic Energy Agency (IAEA) to allow tougher inspections of Iran's nuclear facilities.
The agency has given Iran until the end of the month to provide evidence that it is not trying to build nuclear weapons.
Iran insists that its nuclear programme - which includes uranium-enrichment activities - is designed to meet its energy needs only.
Quid pro quo?
Iranian President Mohammad Khatami is to meet UK Foreign Secretary Jack Straw and his French and German counterparts Dominique de Villepin and Joschka Fischer on Tuesday.
Tehran denies it has a nuclear weapons programme
In a statement, Mr Straw said he would be "impressing upon the Iranian authorities the urgent need for compliance with all of the requirements of the Resolution passed on 12 September by the Board of Governors of the International Atomic Energy Agency."
The IAEA has called on Iran to accept tougher UN inspections by signing an additional protocol to the Non-Proliferation Treaty.
According to diplomats, France, Germany and the UK have been engaged in a secretive effort to convince Iran to sign the protocol.
The three are believed to have offered technical assistance to Iran in exchange for its co-operation.
Mr Khatami on Sunday said Iran would do "whatever may be necessary to solve the problem," provided it retained its rights to have nuclear technology.
If Iran joins the 80 other signatories of the protocol, its nuclear facilities will be liable to snap inspections by the IAEA.
In a BBC interview on Thursday, IAEA head Mohamed ElBaradei spoke of "discussions between Iran and some of the European countries to try to see whether (...) Iran might get assurance of supply" of nuclear fuel.
The agency also wants Iran to provide additional information about its nuclear programme by 31 October.
In particular, the IAEA is seeking clarification on traces of highly enriched uranium found in samples taken by its inspectors at an Iranian nuclear facility earlier this year
Iran insists the traces were the result of contamination on imported equipment.
However Mr ElBaradei has accused Tehran of withholding information to clear up the issue.