Federal authorities searched Wednesday for a man using a Middle Eastern name and possible bogus construction credentials to try to purchase large quantities of the same explosive used by Timothy McVeigh (search) to blow up the Oklahoma City federal building.

The Bureau of Alcohol, Tobacco, Firearms and Explosives (search ) said there is no indication yet that terrorism is involved, but the agency is still checking information that came from a company in Canada that reported the attempted purchase as suspicious.

ATF is asking the fertilizer and explosives industries to help locate the man and to report any suspicious inquiries for the fertilizer chemical ammonium nitrate (search ), which is used to make so-called fertilizer bombs.

"We're still running down leads. But we thought it would be prudent putting out an advisory to the fertilizer industry," said Tom Mangin, an ATF agent in Phoenix, where the investigation is centered.

The suspect also made several Internet email inquiries to vendors seeking to buy between 500 to 1,000 metric tons of the explosive — a quantity larger than McVeigh used to bomb the Oklahoma City federal building in April 1995 but smaller than amounts companies typically might buy in bulk for construction, explosives or farm work.

The International Society of Explosives Engineers (search ), based in Cleveland, sent an e-mail Wednesday alerting its members and asking them to call ATF in Phoenix to report any suspicious activity.

"ATF has recently been made aware of a suspicious attempt by an individual to purchase mass quantities of ammonium nitrate, specifically between 500 to 1,000 metric tons," the alert said. "This individual, who uses a Middle Eastern name, purports to be a representative of a construction corporation. However, indications are that this is most likely false.

"The individual has previously made contact with other industry members via e-mail seeking the large amounts of 'fertilizer grade' ammonium nitrate," the alert said.

Ammonium nitrate has been linked to several recent terror plots.

Less than a year ago, Homeland Security officials put out a warning about unsubstantiated intelligence suggesting that Al Qaeda or like terrorists might try to smuggle ammonium nitrate bombs aboard public transportation venues such as trains, subways or buses.

Jordanian authorities alleged in an indictment last summer that Iraqi insurgency leader Abu-Musab al-Zarqawi (search), backed by Al Qaeda, financed a plot for suicide bombers armed with chemicals for an ammonium nitrate bomb to try to attack the country's intelligence agency building.

And in Chicago, a disgruntled ex-con was charged with plotting to blow up the federal courthouse in downtown after he was arrested during a sting with a pickup truck containing 1,500 pounds of fertilizer he thought was ammonium nitrate. Prosecutors allege he planned to sell the chemical to terrorists.