He told a memorial service in the city the US must "try to find some meaning amidst our sorrow" and could unite.
His trip came amid mounting racial tensions across the country.
Micah Johnson killed the Dallas officers at a protest held over the recent police shootings of African Americans in Minnesota and Louisiana.
Before he was killed by police, he said he was angry about the shootings.
Meanwhile, protests over excessive police force against black Americans have been held in cities across the US.
