Police officers pay their respects ahead of the funeral for Officer Lorne Ahrens in Plano, Texas, US July 13, 2016. [Photo/Agencies]

The funerals came a day after President Barack Obama praised the slain officers' heroism, condemned the attack as an "act not just of demented violence but of racial hatred" and made an impassioned plea for national unity.

The five officers were killed by a former US Army Reserve soldier who told police that he was angry about police killings of two black men in Louisiana and Minnesota earlier that week and wanted to "kill white people," especially police.

Funerals for the other two slain officers, Michael Krol, 40, and Patrick Zamarripa, 32, are expected later in the week.

The shootings in Louisiana and Minnesota were the latest in a series of high-profile police killings of black men in various US cities that have brought intense scrutiny of police use of force, particularly against black suspects.

The officers slain in Dallas last week were patrolling a demonstration decrying the killings by police of Alton Sterling, 37, in Baton Rouge, Louisiana, and Philando Castile, 32, outside St. Paul, Minnesota.