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SANAA, July 5 (Reuters) - At least four people were killed by an explosion near a postal office in Yemen's northern Saada province, a local official said on Saturday.

The cause of the explosion was unknown, he added.

Government forces and Shi'ite rebels loyal to Abdul-Malik al-Houthi have fought intermittently in Saada since 2004. Hundreds of people have been killed and thousands of others have fled their homes.

Yemen, one of the poorest countries outside of Africa, is also grappling with a violent campaign by al Qaeda militants, dwindling oil and water resources, and unemployment. (Reporting by Mohamed Sudam, writing by Ola Galal, editing by Stephen Weeks)

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