President Obama has urged Americans to find "open hearts" as he honoured the police officers killed by a sniper in Dallas in a racist attack.

He spoke near five empty chairs for the police officers killed by a black man seeking vengeance for killings at the hands of white officers.

Dallas Police Chief David Brown (being hugged here by Michelle Obama) spoke directly to the families of those killed:

Former US president George W. Bush, was given a standing ovation after paying tribute to five police officers killed in the city last week: