The Hellfire R9x missile is intended to limit damage compared to typical missiles.
Al Qaeda chief Ayman al-Zawahiri was killed by the US forces in a drone strike in Afghanistan capital Kabul. Announcing his death in a televised address, US President Joe Biden said no civilian casualties were reported in the operation that was conducted over the weekend.
A senior official in the Biden administration was quoted as saying by news agency AFP that Zawahiri was on the balcony of a house in Kabul when he was targeted with two Hellfire missiles, an hour after sunrise on July 31.
According to the official's account, Mr Biden gave his green light for the strike on July 25 - as he was recovering in isolation from Covid-19.
Also Read | How CIA Identified, Killed Al Qaeda Chief Zawahiri
However, pictures from the Kabul home where Zawahiri was living showed no signs of an explosion, pointing to the use again by the US of the macabre Hellfire R9X.
What is the Hellfire 9X?
Also called the "ninja bomb," the missile has become the US weapon of choice for killing leaders of extremist groups while avoiding civilian casualties.
The missile is fired from a Predator drone. It has no warhead, but deploys six blades which fly in at high speed, crush and slice the targeted person.
This is the reason why it's called the "flying ginsu", after the 1980 TV commercial for Japanese kitchen knives that would cut cleanly through aluminum cans and remain perfectly sharp.
Some pictures posted online show the impact of these missiles. One of these old photos on Twitter claims to show a car destroyed by Hellfire R9X in Idlib, Syria.
Pentagon and CIA - the two agencies which undertake targeted assassinations - have never acknowledged the use of the Hellfire R9X missile.
Why these missiles are used in special cases?
According to Wall Street Journal (WSJ), the missiles were born after former US President Barack Obama emphasised on avoiding civilian deaths in US airstrikes in Afghanistan, Pakistan, Iraq, Syria, Somalia, Yemen and other countries.
The R9X variant of Hellfire is used only in specific circumstances, particularly when a terrorist leader has been pinpointed. It is intended to limit damage compared to typical missiles by reducing the risk of killing innocent civilians around the target.
The weapon was under development as early as 2011, the report further said.
Where have they been used before?
Quoting US Defence Department officials, the WSJ report said that the Hellfire missile has been used half a dozen times, including in operations in Libya, Syria, Iraq, Yemen and Somalia.
The Hellfire R9X is a little more than five feet long and weighs just over 100 pounds and doesn't leave behind any signature like burned-out shells or mangled marks.