The US military has found a weapons site 130 miles (208 kilometres) northwest of the capital Baghdad that has tested positive for chemical agents according to American broadcaster ABC News.
Among the materials the military found were fourteen 55-gallon drums, at least a dozen missiles, and 150 gas masks said the television station.
An international team of chemical weapons experts is expected to visit the site near the town of Bayji on Sunday.
A US Special Forces reconnaissance team found the weapons on Friday night.
A platoon of chemical weapons experts from the Army's 110 Cavalry was dispatched immediately to investigate. It took most of the night to secure the area.
On Saturday morning, Lieutenant Valerie Phipps and her squad used three different methods to test liquid from one of the barrels.
The US military said the preliminary tests showed it to be a mixture of three chemicals - including a nerve agent and blistering agent. Phipps says the tests have an accuracy of 98 percent.
Officials say this is could be the most promising find yet in the search for Iraq's weapons of mass destruction. But so far they have tested only one of the 14 barrels.
But the Pentagon is being cautious, telling ABC News that more sophisticated tests would need to be carried out at a lab outside the country.
The barrels are completely unmarked, lying out in the open. Missiles, some still in their shipping containers, are visible nearby. Two specially equipped vehicles were also found in the area.
Looters had already stripped them of their tyres and other portable equipment. But the vehicles' interiors seem to have been left intact. They contain charts listing various dosage levels and work stations, as well as giant mixing devices that appear to be Russian made.
Local residents say the material was dumped at the site by Iraqi troops the day after US forces took Baghdad.
They say an Iraqi officer stayed behind for two more days, because he said the material was too dangerous to leave out in the open.