A top U.S. military commander in Iraq says no evidence has yet surfaced of any weapons of mass destruction despite numerous intelligence tips. But the commander is confident that evidence will eventually be found.

Marine Lieutenant General James Conway says U.S. forces in Iraq continue to receive tips from Iraqis who claim to have knowledge about the location of chemical or biological weapons or components.

General Conway told reporters at the Pentagon U.S. forces continue to send out teams to investigate those claims.

But he said so far the searches have been fruitless. "I will tell you to date we have not had any of those leads turn into anything tangible," he added.

But General Conway remains optimistic evidence will be found of Iraq's weapons of mass destruction program, though he suspects that evidence is probably well-hidden.

"I still think that somewhere out there barrels are buried in the desert," he said. "We recently found Migs buried that we didn't know about so if you contrast that with the difficulty of burying 55 gallon drums, it's certainly within the art of the possible. So I still remain optimistic that we will find out in the long term, based on the people we are rolling up [detaining], interrogations and so forth, that elements of a program existed."

General Conway commanded the nearly 90,000 Marines who took part in Operation Iraqi Freedom, traveling from Kuwait all the way north to Tikrit by the war's end. He has just returned from Iraq after turning over command of much of the south central part of the country to Polish-led multi-national troops. He pointed out that the last U.S. Marines in Iraq should leave by early October, although Army troops will remain.