US border authorities unveiled a new set of guidelines Friday in an effort to drastically reduce instances of agents shooting at moving vehicles or at migrants throwing rocks, reversing a policy that left several dead.

Border Patrol Chief Michael Fisher ordered customs and border agents not to shoot at vehicles when their occupants are fleeing and also barred officials from placing themselves in the path of a vehicle or using their body to block its path.

Fisher also demanded that agents seek cover or move away from rock throwers, and only shoot when facing "imminent danger of death or serious physical injury to the agent or another person."

According to the Inter-American Commission on Human Rights, at least 28 migrants have been killed along the US border with Mexico since 2010.

The new rules were listed in a four-page memorandum on the use of lethal force on the US borders with Mexico, chiefly, and Canada, following a special commission that investigated the use of firearms.

Secretary of Homeland Security Jeh Johnson, who took office in December, had ordered the Border Patrol to revise its directives on the use of lethal force against unarmed civilians along the borders.

Fisher's directive will "lessen the likelihood of deadly force situations as we meet our dual goals of ensuring the safety and security of our dedicated agents as well as the public that they serve," Johnson said.

Between 2010 and 2012, no less than 67 incidents of gunshots were recorded, most of them on the border with Mexico, which is fighting a scourge of violence related to the trafficking of illegal drugs to the lucrative US market.