The officials say it's unclear who was behind the pre-dawn attack Tuesday. The officials spoke on condition of anonymity because they are not authorized to talk to the media.
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The attack is likely to stoke tensions hours before rival mass rallies by opponents and supporters of President Mohammed Morsi over the country's new constitution.
The liberal opposition says the draft charter restricts freedoms and gives Islamists vast influence over running the country.
The draft, adopted by Morsi's Islamist backers late last month, is going to a referendum on Saturday. It has vastly polarized the nation and triggered some of the worst violence since Morsi took office.
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