The smuggling of stolen antiquities from Iraq's rich cultural heritage is helping finance Iraqi extremist groups, says the U.S. investigator who led the initial probe into the looting of Baghdad's National Museum.

Marine Reserve Col. Matthew Bogdanos claimed both Sunni insurgents such as al-Qaida in Iraq and Shiite militias are receiving funding from the trafficking.

Bogdanos, a New York assistant district attorney, noted that kidnappings and extortion remain the insurgents' main source of funds. But he said the link between extremist groups and antiquities smuggling in Iraq was "undeniable."

"The Taliban are using opium to finance their activities in Afghanistan," Bogdanos told The Associated Press in an interview during a two-day UNESCO-organized conference that ended Tuesday on returning antiquities to their country of origin.

"Well, they don't have opium in Iraq," he said. "What they have is an almost limitless supply of is antiquities. And so they're using antiquities."