UN peacekeepers said Israeli fire on their headquarters in south Lebanon Thursday left two Blue Helmets injured, sparking condemnation from European members of the mission.
Italy said the acts "could constitute war crimes".
It is the most serious incident reported by the peacekeeping mission since it said last week it had rejected Israeli demands to "relocate" from some of its positions.
UNIFIL, which has about 10,000 peacekeepers stationed in south Lebanon, has called for a ceasefire since an escalation between Israel and Lebanese militant group Hezbollah on September 23, after a year of cross-border fire.
"This morning, two peacekeepers were injured after an IDF Merkava tank fired its weapon toward an observation tower at UNIFIL's headquarters in Naqura, directly hitting it and causing them to fall," the mission said, using an acronym for the Israeli military.
The peacekeepers did not suffer serious injuries, "but they remain in hospital," it said.
A UNIFIL spokeswoman said they were Indonesian.
The defence minister of Italy, which along with Indonesia is among UNIFIL's largest troop contributors, said the attack and other incidents UNIFIL blames on Israel "could constitute war crimes", and had asked for an explanation because "it was not a mistake".
Guido Crosetto described the "shooting" as "intolerable" and said he "protested to my Israeli counterpart and the Israeli ambassador to Italy".
The French foreign ministry also said it expected "explanations from the Israeli authorities" after the incident, adding: "The protection of UN peacekeepers is an obligation for all parties in a conflict".
Spain's foreign ministry said it "strongly condemns the Israeli firing that hit the UNIFIL headquarters" which it called a "grave violation of international law".
- 'Reckless' -
Irish Prime Minister Simon Harris, whose country has about 370 troops in the mission, said "any firing in the vicinity of UNIFIL troops or facilities is reckless and must stop".
According to UNIFIL, the Israeli military also hit another position in Ras Naqura, further to the south, on Thursday.
UNIFIL said it hit "the entrance to the bunker where peacekeepers were sheltering, and damaging vehicles and a communications system".
The mission added that an Israeli military drone "was observed flying inside the UN position up to the bunker entrance."
UNIFIL headquarters and nearby positions "have been repeatedly hit," the mission said.
On Wednesday, "IDF soldiers deliberately fired at and disabled" perimeter-monitoring cameras around a position, UNIFIL added.
UNIFIL last week said the Israeli military, before it began ground operations inside Lebanon, had asked the peacekeepers to "relocate" from some positions.
The peacekeeping mission rejected the demand, which Ireland's President Michael Higgins, called "an insult to the most important global institution".
- 'Extremely dangerous' -
On Sunday UNIFIL warned that Israeli operations near one of its positions southeast of Maroun al-Ras were "extremely dangerous" and compromising the Blue Helmets' safety.
Maroun al-Ras is about 27 kilometres (17 miles) east of Naqura.
Israel has pounded what it says are Hezbollah positions in Lebanon in the past two weeks, killing more than 1,200 people and displacing more than a million people from their homes, according to official figures.
It has said it is carrying out "limited" incursions across its northern border, while Hezbollah has repeatedly said it was firing on Israeli soldiers trying to advance in the area.
Earlier on Thursday, Hezbollah said that it has destroyed an Israeli tank advancing towards Ras al-Naqura, and fired rockets at Israel troops in another Lebanese area along the frontier, Mais al-Jabal.
It also said it launched rockets at several areas in northern Israel, including one area north of the city of Haifa.
UNIFIL was set up in 1978 to monitor the withdrawal of Israeli forces after they invaded Lebanon in reprisal for a Palestinian attack.
It was bolstered in Security Council Resolution 1701 after Hezbollah and Israel fought a war in 2006, and its peacekeepers are tasked with monitoring the ceasefire between the two sides.