Federal investigators have searched a Minnesota vegetable farm but details on why remain sketchy.

KMSP-TV reports a helicopter and at least a dozen unmarked SUVs and cars surrounded the house and another dozen surrounded a warehouse Thursday on the Svihel Vegetable Farm in Foley, owned by John and Julie Svihel.

John Svihel told the station he was surprised and all of his migrant workers were there legally. He said none were taken away. However, he said investigators did seize computers and boxes of files.

The operation was led by the State Department's Bureau of Diplomatic Security, which investigates passport and visa fraud.

DS spokesman Alan Silverlieb declined comment and referred questions to the U.S. attorney's office, which also declined comment.

The Svihels did not immediately return a call Friday.