Five US soldiers are charged with deliberately targeting Afghan civilians amid growing discontent over the rising civilian causalities in the war-torn country.
The troopers allegedly killed three Afghans in Kandahar Province this year and they were charged with murder in June.
Since then US army prosecutors have also filed additional charges of conspiracy to commit premeditated murder -- a plot that allegedly began when one soldier discussed how easy it would be to "toss a grenade" at Afghan civilians, The Seattle Times reported on Thursday.
One of the soldiers had reportedly formed what has been called a "kill team" to randomly execute Afghan civilians while on petrol.
Investigators say anyone who dared to report the events was threatened with violence. All five are awaiting court martial and could face life in prison or death if convicted.
Analysts say it could be one of the most serious war-crimes cases to emerge from the Afghan war.
A recent UN report says that nearly 1,300 civilians were killed by NATO or Afghan forces in the first six months of 2010.
Civilians have been the main victims of violence in Afghanistan, particularly in the country's troubled southern and eastern provinces.
The issue of civilian casualties has caused friction between Washington and the Afghan government.