CAIRO (Reuters) - At least 24 Egyptian policemen were killed and three wounded in an ambush by Islamist militants on Monday near the north Sinai town of Rafah, medical and security sources said.

The policemen were on their way to their barracks in Rafah, near the border with Israel, when militants attacked them with machineguns and rocket-propelled grenades, the security sources said. Earlier reports had said an explosion caused the casualties.

Attacks by Islamist militants in the lawless north Sinai region have intensified since the army overthrew Islamist President Mohamed Mursi on July 3.

At least 850 people, including 70 police and soldiers, have been killed in the past week in a crackdown on Mursi's Muslim Brotherhood, which says it renounced violence decades ago.

(Reporting by Asma AlSharif; Editing by Alistair Lyon and Janet Lawrence)

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