Alireza Jafarzadeh claimed the information came from the same sources that led to his revelation in May 2003 that Iran had a clandestine nuclear program.
Iran's UN Mission called the allegation "baseless and unfounded".
Mr Jafarzadeh said his sources had told him about the laser enrichment program at Lashkar Ab'ad, about 25 km north-west of Tehran.
He heads the Washington-based Strategic Policy Consulting think tank and is credited with having aired Iranian military secrets in the past.
Despite this US officials consider some of his assertions to have been inaccurate.
Mr Jafarzadeh urged the International Atomic Energy Agency to immediately send UN nuclear inspectors to Lashkar Ab'ad and demand access to all areas.
In particular a new 460 square metre hall in a large garden where he said secret laser enrichment activities are being conducted.
IAEA spokeswoman Melissa Fleming said the body had only just been sent a copy of the report and said "like all information that we receive, we must take the time to check it against all our information in order to decide whether it is worth following up".
Ahmadinejad gets NAM backing
In Havana, Iran's President Mahmoud Ahmadinejad has drawn firm backing for Tehran in the tense standoff over its nuclear program from a summit of leaders of developing country.
His trip to Cuba came as the United States pushed for sanctions against Iran, which has ignored an August 31 UN deadline to stop enriching uranium.
As his delegation lobbied for further support from the 118 NAM member states, Mr Ahmadinejad held meetings with several of his counterparts on the sidelines of the September 11-17 Non-Aligned Movement meeting.
He drew strong backing from Venezuelan President Hugo Chavez during a summit of 18 developing countries (G-15) held in parallel to the NAM gathering Thursday. "I don't want to leave here until there is decisive support for Iran," the South American leader said.
Leaders of the NAM countries were expected to adopt a statement which stresses Iran's right to acquire and use nuclear energy and technology for peaceful means.
In Washington the White House dismissed Iran's calls for unconditional negotiations. "We can't be any more clear about this; suspend enrichment and reprocessing activities and we'll talk," said White House spokesman Tony Snow.