(CNN) — Two men are in custody after a police officer was shot in the head while responding to a robbery in Mississippi, authorities said.

The officer, who works for the Clarksdale Police Department, is in critical condition after the shooting Saturday night, Mayor Bill Luckett said.

The alleged shooter and his accomplice turned themselves in Sunday, hours after the shooting in Clarksdale.

Suspicious activity

The men were robbing the store when the officer, who was nearby, noticed suspicious activity there, according to the mayor. Two clerks fled through the back door.

The men stole money from a cash register and took off, Luckett said.

Officer shot

The officer caught up with the robbers four blocks from the store, where they shot him and left him bleeding on the street, the mayor said.

At least one of the assailants had a gun, he said.

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