ISTANBUL—The respected editor of a prominent Turkish newspaper and one of his key reporters have been detained, jailed and accused of espionage for a controversial story about an alleged arms shipment from Turkish intelligence to Syrian rebels.

Turkish authorities on Thursday imprisoned Can Dündar, editor in chief of Cumhuriyet, and Erdem Gül, the newspaper’s capital correspondent in Ankara, on charges of spying and aiding a terrorist organization, the newspaper’s attorney said. If convicted, the two men would face life in...