Aug 17 (Reuters) - U.S. President Donald Trump on Monday said he approved federal disaster aid for Iowa after a hurricane-force storm hit last week, causing widespread damage in towns and farms and leaving thousands without power.

Iowa Governor Kim Reynolds said on Sunday she requested about $4 billion in emergency funds following the Aug. 10 storm.

The destruction compounded troubles for a U.S. agricultural economy already battered by extreme weather, the U.S.-China trade war and disruptions to labor and food consumption from the COVID-19 pandemic.

"I just approved an emergency declaration for Iowa," Trump told reporters at the White House before departing on a trip to the Midwest. "It really did a lot of damage," he said of the storm.

Trump, who is scheduled to speak on Monday in Minnesota and Wisconsin, said he aimed to visit Iowa.

"I'll be going very soon and maybe today," he said.

Media reports said the storm caused at least three deaths in Iowa. Winds as high as 100 miles per hour (160 kph) hit eastern Nebraska, Iowa, Wisconsin and parts of Illinois.

The storm impacted 37.7 million acres of farmland across the Midwest, including 14 million in Iowa, the Iowa Soybean Association said on Friday, citing estimates from the U.S. Department of Agriculture.

"I've never seen the corn flattened as much as it has from this terrific windstorm," U.S. Senator Charles Grassley of Iowa told reporters on Monday. "The number of grain bins flattened is humongous."

The storm affected 58,000 holders of crop-insurance policies with a liability of around $6 billion in Iowa, according to the Iowa Soybean Association.

Grassley said crop insurance covers about 90% of Iowa farmland. It is too early to determine whether there will be enough storage space for the autumn harvest, he said.

(Reporting by Kanishka Singh in Bengaluru; Steve Holland in Washington; and Tom Polansek in Chicago; Editing by Nick Macfie and Dan Grebler)