The man who shot dead five police officers in Dallas and wounded seven more was planning an even larger attack, the city’s police chief says.

Micah Johnson, 25, was angry with the recent killings of black men by police and wanted to kill white officers, police say.

Police chief David Brown said he was “convinced” Johnson had wider plans.

He told CNN that Johnson, a military veteran, appeared to have practised detonating explosives.

Mr Brown also said police were trying to find the significance of the letters ‘RB’ that Johnson had written in his own blood, near where he was killed by a remote detonation by police.

Officers were also reading a journal found in Johnson’s house that Mr Brown said was proving “hard to decipher”.