Six Hezbollah fighters were killed in the raid near Quneitra on the Syria-controlled side of the Golan Heights.
An Israeli security source told AFP that an Israeli helicopter carried out the strike but the UN account raised the possibility that drones may have been used.
UN spokesman Farhan Haq said the UN observer force in the Golan on Sunday "observed two unmanned aerial vehicles flying from the Alpha (Israeli) side and crossing the ceasefire line."
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"An hour later, smoke was observed coming from the general direction of position 30," Haq told reporters.
UN peacekeepers then saw the drones flying over the area of "position 30" and again crossing the ceasefire line, he added.
"The incident is a violation of the 1974 agreement on disengagement" between Israel and Syria, he added.
Among Hezbollah's dead was Jihad Mughniyeh, the son of an assassinated commander from the group, and Mohammed Issa, a commander responsible for Hezbollah's operations in Syria and Iraq.