UN peacekeepers said Israeli fire on their headquarters in south Lebanon Thursday injured two Blue Helmets, sparking condemnation from European members of the mission.
Israel acknowledged its forces had opened fire in the area, saying the Hezbollah militants on whom it is waging an escalating war operate near UN posts.
Italy, a major contributor of troops to the force, said the acts "could constitute war crimes" while Washington said it was "deeply concerned."
The incident came after the peacekeeping mission last week 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 from Indonesia, a major contributor of troops to UNIFIL.
Indonesia's UN ambassador Hari Prabowo said the incident "clearly demonstrates how Israel positioned itself above international law, above impunity and above our shared values of peace."
Israel said its military "opened fire in the area" of the UNIFIL base after telling UN forces to seek shelter.
Italy's defence minister said the attack and other incidents UNIFIL blames on Israel "could constitute war crimes", and asked for an explanation because "it was not a mistake".
Guido Crosetto described the "shooting" as "intolerable," lodging protests with his Israeli counterpart and the country's ambassador to Italy.
In Washington, the White House was "deeply concerned", a National Security Council spokesperson said Thursday.
"We understand Israel is conducting targeted operations near the Blue Line to destroy Hezbollah infrastructure... it is critical that they not threaten UN peacekeepers' safety and security."
Spain's foreign ministry said it "strongly condemns the Israeli firing that hit UNIFIL headquarters" which it called a "grave violation of international law".
- 'Serious risk' -
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".
UNIFIL said Israel had also hit "the entrance to the bunker where peacekeepers were sheltering... 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" perimetre-monitoring cameras around a position, UNIFIL added.
The head of UN peacekeeping Jean-Pierre Lacroix said peacekeepers were at "serious risk" and that by Sunday 300 Blue Helmets were temporarily relocated to larger bases "with the movement of another 200 planned."
UNIFIL's footprint in the most affected positions would be slashed by 25 percent, he said.
"The safety and security of peacekeepers is now increasingly in jeopardy," Lacroix told the UN Security Council Thursday.
- 'Extremely dangerous' -
Israel has pounded what it says are Hezbollah positions in Lebanon in the past two weeks, killing more than 1,200 and displacing more than a million, 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 it had destroyed an Israeli tank advancing toward Ras al-Naqura, and fired rockets at Israeli 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 by 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.