The agent was intentionally run down by a Hummer Saturday while laying spike strips about a mile from the Mexican border, The San Diego Union-Tribune reported Sunday.
"The Hummer sped up and swerved toward our agent, killing him," Eric Anderson, a spokesman for the agency's Yuma sector, told the newspaper.
The incident began when agents saw a brown Hummer and a red Ford F-250 pickup crossing from Mexico into the United States about 20 miles west of Yuma.
"We don't know if they were smuggling people or drugs," Anderson said.
After the agent was struck, both vehicles escaped into Mexico. Mexican authorities are cooperating in the search for the suspects, Anderson said.