Authorities say the officers were ambushed as they sat in their patrol cars in Des Moines in Iowa in separate attacks.

Police quickly named Scott Greene as a suspect.

The man is reported to have had a recent run-in with the police after holding up a controversial Confederate battle flag at a sports stadium.

The flag is associated with the pro-slavery south in the US civil war.

The officers were found dead in their vehicles about three kilometres apart in the early hours of Wednesday. (Euronews)