Iran could bring negotiations with the European Union to a sudden end by resuming parts of its nuclear programme as soon as next week, European diplomats have warned.

EU officials are working on the final details of an offer to assist Tehran in the nuclear, economic and diplomatic fields, as long as it turns its back on technologies that could be used for nuclear weapons. But recent Iranian statements have stoked European fears that Tehran could be about to resume activity at its uranium conversion plant, with a preliminary role in the nuclear fuel cycle.