The US government is trialling a new open-source system to count killings by police around the country, in the most comprehensive official effort so far to accurately record the number of deaths at the hands of American law enforcement.

The pilot program was announced by the US attorney general, Loretta Lynch, on Monday and follows concerted calls from campaigners and lawmakers for better official data on police killings, after a nationwide debate about race and policing was sparked by protests in Ferguson, Missouri, in 2014.