The United Nations has said four of its military observers were wounded when a shell exploded near them in southern Lebanon, AFP reports.

The United Nations Truce Supervision Organization (UNTSO) did not identify the source of the shelling, but Lebanon’s official National News Agency blamed Israel.

“This morning four UNTSO military observers on a foot patrol along the Blue Line (demarcating the border with Israel) were injured when a shell exploded near their location,” UNTSO said.

“The targeting of peacekeepers is unacceptable,” it said in a statement, adding that the peacekeepers were taken to hospital for treatment and an investigation was launched into the origin of the explosion.