Col. John Peabody, engineer brigade commander of the 3rd Infantry Division, said the materials were found Friday at the Latifiyah industrial complex just south of Baghdad.
"It is clearly a suspicious site," Peabody said.
CBS News National Security Correspondent David Martin reports that the hunt for weapons of mass destruction continues at sites where the U.S. thought chemicals weapons might be hidden.
"And although there are no reports of actual weapons being found, there are constant finds of suspicious material," Martin said. "It obviously will take laboratory testing to find out exactly what that powder is."
The senior U.S. official, based in Washington and speaking on condition of anonymity, said the material was under further study. The site is enormous and U.S. troops are still investigating it for potential weapons of mass destruction, the official said.
"Initial reports are that the material is probably just explosives, but we're still going through the place," the official said.
Peabody said troops found thousands of boxes, each of which contained three vials of white powder, together with documents written in Arabic that dealt with how to engage in chemical warfare.
He also said they discovered atropine, used to counter the effects of nerve agents.
The facility had been identified by the International Atomic Energy Agency as a suspected chemical, biological and nuclear weapons site. U.N. inspectors visited the plant at least nine times, including as recently as Feb. 18.
The facility is part of a larger complex known as the Latifiyah Explosives and Ammunition Plant al Qa Qaa.
During the 1991 Gulf War, U.S. jets bombed the plant.
Troops also discovered what they believe is a training center for nuclear, chemical and biological warfare in Iraq's western desert, Brig. Gen. Vincent Brooks said Friday.
One bottle found at the site was labeled "tabun" — a nerve agent that the U.S. government says may have been used during the 1980-88 Iran-Iraq war. The soldiers found only a small amount of the chemical, indicating the site was meant for training, not storing or deploying chemical weapons, Brooks said.
"In that particular site, we believe that was the only sample," Brooks said. "That's why we believe it was a training site. Our conclusion is that this was not a (weapons of mass destruction) site ... it proved to be far less than that."
Photos of the site showed shelves of brown bottles with yellow labels. Brooks said troops did not understand some of the labels and were collecting the bottles for examination by experts.
On April 1, Iraqi Vice President Taha Yassin Ramadan, in a statement on Iraqi television, repeated Baghdad's position that it had no weapons of mass destruction. Referring to reports that gas masks and other chemical gear had been found elsewhere in the country, he said the coalition might plant weapons of mass destruction to implicate Iraq.
"Let me say one more time that Iraq is free of weapons of mass destruction," he said.
"The aggressors may themselves intend to bring those materials to plant them here and say those are weapons of mass destruction," he said.