President Barack Obama has led tributes to five Dallas police officers killed during a sniper attack last week.
He told a memorial service that the United States must "reject despair" at a time of heightened racial tensions across the country.
President Obama said that although racism still existed in America, the country had made remarkable progress during his lifetime.
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President Obama said it was vital to heal the divide between police and some communities.
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Former President George W. Bush also spoke at the ceremony. He praises the courage of the slain police officers.
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Dallas Police Chief David Brown quoted Stevie Wonder's song 'As' during his tribute to the slain officers.
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