She said: "We are aware of the US statement about the airstrike targeting Mohammed Emwazi. Like them, we are not commenting further at this stage."
Mr Haines, an aid worker from Scotland, was executed in September last year, having been held captive for 18 months.
His daughter Bethany later said she felt families of Emwazi's victims would only feel closure "once there's a bullet between (his) eyes".
A video released a month later showed 47-year-old Salford taxi driver Mr Henning appearing to be beheaded.
His daughter Lucy said she found out he had been killed when she saw an image posted on social media site Instagram.
Emwazi appeared in the videos dressed in black with only his eves visible, and spoke with a British accent as he went on anti-western rants to the camera while wielding a knife.
It emerged that he had been known to British intelligence services, but managed to travel to Syria in 2013.