An Iranian presidential aide said Wednesday the country will not stop its nuclear work despite the U.S. demand for it to be halted based on U.N. resolutions, Reuters reported.

The statement comes as an International Institute for Strategic Studies (IISS) report says Iran will have enough enriched uranium to make a single nuclear weapon later this year.

The think tank made the prediction in its 'Military Balance 2009,' an annual assessment of global defense and military developments.

Announcing the new report on Tuesday, Mark Fitzpatrick said the threat may not necessarily be as big as it sounds.

"Being able to enrich uranium is not the same as having nuclear weapons," he said.

In addition, the report placed doubts over U.S. intelligence estimates that Iran halted its work on nuclear weapons six years ago and pointed to Tehran's continued development of long-range ballistic missiles able to reach targets in Israel and beyond.