WASHINGTON—The Homeland Security Department has fired an employee who runs a website predicting and advocating a race war, about four months after he was put on paid administrative leave.

Ayo Kimathi was an acquisitions officer for Immigration and Customs Enforcement who dealt with small businesses. He also runs the website War on the Horizon, which includes descriptions of an "unavoidable, inevitable clash with the white race." Kimathi is black. He goes by the online pseudonym "Irritated Genie."

In a brief statement, the department said Kimathi's last day was Dec. 6.

Kimathi said in an email that he was proud of his work at ICE and predicted that fewer small businesses would win contracts after his firing.