© Fotolia/ Dominik Herz
Aside from self-defense, some US states allow police officers to use weapons to suppress opposition to arrest and control crowd violence.

"The United States has failed to track how many people are killed by law enforcement officers. No-one knows exactly how many people are killed each year but estimates range from 400 to over 1,000," the Amnesty International USA stated in the report.

People of African-American descent and those with darker skin color in the United States often fall victim to a disproportionate use of lethal force by police, the human rights group highlighted.

"African-Americans are disproportionately impacted by police killings... While blacks represent 13.2 per cent of the US population, they represent 27.6 per cent of the total deaths at the hands of police (6,338) included in the data on violent deaths recorded by the Center for Disease Control between 1999 and 2013," the report revealed.

Killings by police occur, to a large extent, because of a failure to comply with international law and standards on the use of lethal force by law enforcement officers in the United States, according to the report. Nine states and Washington DC have no laws regulating the use of lethal force by police.

Over the past year, the United States experienced a series of protests and rallies against well-documented police brutality in the country. Mass actions, some violent, were triggered by a series of killings of unarmed blacks by white police officers.