As Eugene Kontorovich’s (of Jerusalem-based Kohelet Policy Forum and George Mason University Scalia Law School) in his lede notes,

[A]s Israel fights Hezbollah’s army in Lebanon, it has found a new foe: the United Nations Interim Force in Lebanon. Having failed at its mission of neutralizing the Hezbollah threat, Unifil is now actively interfering with Israel doing the job.

Never mind that, per the UN’s Security Council, UNIFIL’s mandate includes

ensuring that no “armed groups” operate in southern Lebanon

Those barred armed groups include Hezbollah. Instead, UNIFIL

has allowed Hezbollah to entrench itself in southern Lebanon over the years, storing arms in many of the homes and building a network of fully stocked attack tunnels and small outdoor weapons depots in preparation for an Oct. 7-style assault. Israeli troops have found a tunnel about 100 meters from a Unifil outpost.
For 11 months Hezbollah fired more than 8,500 rockets and missiles at Israel, mostly from southern Lebanon, under Unifil’s nose. The area, militia-free by order of the UN Security Council, was soon crawling with the world’s best-armed terrorists. But the peacekeepers said little and did less.

Not just 100m away. In the IDF’s current move into southern Lebanon,

Israeli forces discovered Hezbollah tunnel entrances abutting Unifil posts.

Kontorovich is being generous. UNIFIL has not failed. It has been succeeding, in its internally defined mission to support Hezbollah and to operate against Israel.

Thus, war crimes. UNIFIL, via its conscious decision to abrogate its assignment of keeping Hezbollah out of southern Lebanon, and its equally conscious decision to shield Hezbollah politically and lately to attempt physical shielding, is the one committing war crimes. UNIFIL’s guilt is made manifest by its decision to allow Hezbollah to build tunnels for attacking Israel right up against UNIFIL buildings to contribute to those tunnels’ disguise.

UNIFIL is not the only entity guilty of war crimes, though. UN Secretary General António Guterres shares that guilt with his open support for UNIFIL, and for UNRWA, many of whose members are part of the planners for Hamas’ 7 Oct 23 atrocity and ensuing atrocities throughout the last year, and through them his personal support for terrorists and the terrorists’ atrocities.