US President Barack Obama spoke in Dallas on Tuesday to offer comfort to relatives of the five police officers slain in a sniper ambush -- and to try to unify a nation struggling to process a raw week of deadly violence and racial tensions.

US police shootings: Obama seeks to repair tensions at Dallas memorial service

US President Barack Obama spoke in Dallas on Tuesday to offer comfort to relatives of the five police officers slain in a sniper ambush -- and to try to unify a nation struggling to process a raw week of deadly violence and racial tensions.