By Tom Polansek

June 6 (Reuters) - Missouri authorities are investigating a fake press release about the damaging livestock pest New World screwworm that sparked a selloff in U.S. cattle futures markets last week, the state's agriculture department said on Friday.

U.S. agriculture officials and farmers are on high alert for screwworm as it has moved north in Mexico from Central America, arriving within about 700 miles (1,125 km) of the Texas border.

The U.S. Department of Agriculture indefinitely halted U.S. cattle imports from Mexico last month in a bid to keep out the parasite, which eats livestock and other wild animals alive. Screwworm infestations can kill cattle if left untreated and make them susceptible to secondary infections.

On May 27, a false press release was sent to a northwest Missouri radio station about screwworm, the Missouri Department of Agriculture said.

A report on the radio station's website pressured Chicago Mercantile Exchange cattle futures before being taken offline, livestock traders said. Live cattle futures LCQ25 fell nearly 2% before paring losses, as daily trading volumes in the market spiked 77% from a week earlier.

The Missouri State Highway Patrol's Rural Crimes Investigative Unit, the Livestock and Farm Protection Task Force, and state attorney general are investigating the matter, Missouri's agriculture department said in a press release.

State officials want to determine "if this was an act with malicious intent to cause panic in agricultural markets," the department added.

U.S. cattle producers' group R-CALF USA last week asked the Commodity Futures Trading Commission, which regulates futures markets, to investigate.

The commission did not immediately respond to a request for comment, and exchange operator CME Group CME.O declined to comment.

(Reporting by Tom Polansek in Chicago; Editing by Lisa Shumaker)

((Thomas.Polansek@thomsonreuters.com))