A previously unknown group, Youth of the Resistance, claimed responsibility for the shooting in a statement published on Monday in the Beirut daily An-Nahar.
The unnamed soldier with the UN Interim Force in Lebanon (UNIFIL) was shot twice on Sunday in Naqura where the force has its headquarters. He died in hospital in the southern Lebanese town of Sidon.
UNIFIL spokesman Milos Steiger said an investigation was underway into what was the first incident of its kind since the May 2000 Israeli withdrawal from south Lebanon after two decades of occupation.
"The Youth of the Resistance have shown that they refuse to
allow anyone to help the Israeli enemy, especially by dismantling the explosive devices that the resistance lays along the border" with Israel, the group said.
"We want this incident to serve as a warning to all those
peacekeepers deployed in the border zone, so they do not overstep their mandate and serve the enemy," it said.
The authenticity of the statement was not immediately clear.
UNIFIL was set up in March 1978 to oversee an Israeli withdrawal from south Lebanon that finally took place 22 years later. It is made up of 2000 soldiers and 500 civilians mandated to supervise the ceasefire on the border.
Lebanon refuses to send troops to the border, claiming that
Israel still holds a portion of its territory, and the area is
effectively under the control of the Lebanese Hizb Allah movement.