Corporal Luke Tamatea, 31, and colleagues Lance Corporal Jacinda Baker, 26, and Private Richard Harris, 21, died when their Humvee was hit by a bomb at 9.20am on Sunday (4.50pm NZT).
Less than two weeks before his death, Tamatea posted criticism of Key on Facebook over the Prime Minister's decision not to attend the funeral service of Lance Corporals Pralli Durrer and Rory Malone, who died earlier this month.
The 26-year-olds, who were part of the same deployment as the latest soldiers to die, were killed by insurgents in Bamiyan Province on August 4 after a fierce three-minute gun fight.
Key was not in attendance at Malone's and Durrer's funeral on August 11 as he had a pre-arranged trip to the United States to watch his son Max play in the first New Zealand under-17 baseball team to ever play in the World Series. He was also widely condemned by the NZ public as well.