The death brings to seven the number of UNIFIL peacekeepers killed since the latest conflict erupted in March.

"A UNIFIL peacekeeper died early this morning from critical injuries sustained when mortar shells struck his position," a statement from the force said, adding that two other Blue Helmets were wounded in the incident on Wednesday night.

It said a probe had been launched and also urged "relevant national authorities to investigate the incident".

Serbia's defence ministry said in a statement that "Senior Sergeant Milovan Jovanovic was given emergency medical care at a hospital inside the base after being wounded and then transported by helicopter to the University Medical Centre in Beirut, where he died".

According to UNIFIL, around 170 Serbian peacekeepers are among the 7,500-strong force, whose personnel come from nearly 50 countries.

Peacekeepers are deployed in south Lebanon near the Blue Line, the 120-kilometre (75-mile) de facto border between Lebanon and Israel, where they are in the middle of the fighting.

"UNIFIL has detected an increasingly high number of trajectories and impacts in south Lebanon," the force's statement said, adding that "the violence must end".

In late March, an Indonesian peacekeeper was killed and another later died of his wounds after a projectile hit their base, with a preliminary UN investigation blaming an Israeli tank shell.

Shortly after, two more Indonesian Blue Helmets were killed by an improvised explosive device, which the same UN investigation found was likely planted by Hezbollah.

In April, two French peacekeepers were killed in an ambush that French authorities and the UN attributed to Hezbollah, which denied involvement.

On Monday, UN chief Antonio Guterres said peacekeepers would still be needed in Lebanon after UNIFIL's mission expires at the year's end -- a suggestion likely to face opposition from the United States and Israel.