The U.N. peacekeeping mission in Lebanon (UNIFIL) said a peacekeeper was killed when a projectile exploded at one of its positions near the southern Lebanese village of Adchit al-Qusayr on Sunday.
Another peacekeeper was critically injured, it said in a statement early on Monday.
"We do not know the origin of the projectile. We have launched an investigation to determine all of the circumstances," UNIFIL added.
UNIFIL is stationed in southern Lebanon to monitor hostilities along the demarcation line with Israel - an area that is at the heart of clashes between Israeli troops and Hezbollah group.
The mission, which will be halted at the end of 2026, has been sporadically caught in the crosshairs of both Israel and Hezbollah over the last couple of years. Recent incidents underscored the risks.
On March 6, Ghana's armed forces said the headquarters of its U.N. peacekeeping battalion in Lebanon was hit by missile attacks, leaving two soldiers critically injured.
Israel's military later acknowledged that its tank fire had hit a U.N. position in southern Lebanon that day, wounding the Ghanaian peacekeepers.
The military said its troops had responded to anti-tank missile fire from Hezbollah, which had moderately wounded two of its soldiers.
"Once again, we call on all actors to uphold their obligations under international law and to ensure the safety and security of UN personnel and property at all times, including by refraining from actions that may put peacekeepers in danger," UNIFIL said.