Adds comments from FTC chairman, background

By Tom Polansek

CHICAGO, May 28 (Reuters) - The U.S. Federal Trade Commission said on Thursday it has been investigating increased fertilizer prices following a spike due to the war in Iran.

Soaring prices for fertilizer and fuel due to the conflict have pinched farmers as they plant crops such as corn and grapple with a resurgent drought in parts of the U.S. Plains. Some growers are facing a fourth straight year of shrinking margins.

The Middle East is a leading hub for fertilizer production, and much of the global fertilizer trade typically passes through the Strait of Hormuz, which has seen traffic stalled by the war.

"The commission some time ago commenced a major industry-wide investigation into the precipitous rise of fertilizer prices in this country, which has affected so many of our nation's farmers," FTC Chairman Andrew Ferguson said in a recording of an event with farmers in Texas. The agency confirmed his remarks.

The FTC said the investigation includes the issuance of a civil investigative demand, a type of administrative order that can be used to obtain documents or testimony.