CAIRO, July 5 (Reuters) - Two Egyptian police officers were shot dead on Friday by unknown gunmen in the Sinai town of El-Arish in front of a government building, medical sources said, the latest of a string of security incidents in the lawless region.

The police officers were guarding the building when the gunmen shot at them, the sources said.

Islamist gunmen attacked armed forces guarding the El-Arish airport early on Friday. It was not clear whether the attack, and another on a police station in the nearby town of Rafah, on the Gaza border, were in reaction to the army's overthrow of elected Islamist President Mohamed Mursi on Wednesday. 

(Reporting By Yousri Mohamed; Writing by Maggie Fick; Editing by Alastair Macdonald)