A Greek police officer shot and seriously wounded a private security guard outside the U.S. Embassy in central Athens, authorities said.

The Brinks Security employee, who was hired by the embassy, is listed in serious condition. Police say the 31-year-old Greek national was shot in the neck.

Greek authorities say the shooting didn't appear to be accidental, as initially believed. The police officer involved in the shooting has been taken into custody for questioning. He has not been charged.

Police say the officer fired off two shots and that his explanations for the shooting so far are "unconvincing."

U.S. embassy officials said they were working with Greek authorities to investigate the shooting.