The incident took place north of the Blue Line on Sunday morning and led to the suspension of more than a dozen UN peacekeeping activities for over nine hours, according to UN Spokesperson Stéphane Dujarric.

Toxicology tests

“The IDF said that peacekeepers should stay clear of the area,” Mr. Dujarric told reporters in New York. He added that peacekeepers had supported the Lebanese army in collecting samples dropped, for a toxicology report.

As of Monday afternoon, the test results had not been received.

The Blue Line stretches for approximately 120 kilometres along Lebanon’s southern frontier and serves as a “line of withdrawal” confirming Israel’s withdrawal from southern Lebanon.

The UN reiterated concerns about flight movements across the Blue Line, saying such activities violate Security Councilresolution 1701, which brought an end to the 2006 hostilities between Israel and Hezbollah, and outlines UNIFIL’s mandate.

The latest cessation of hostilities agreement between the two sides was signed in November 2024, after violence flared between Hezbollah and Israeli across the Blue Line following the commencement of the Gaza war.

“Any activity that may put peacekeepers and civilians at risk is of serious concern,” Mr. Dujarric said. “We reiterate our call on all parties to fully comply with their obligations under resolution 1701.”

Wider concerns

The UN Interim Force in Lebanon (UNIFIL) said the incident also raised concerns about the potential impact of the unidentified substance on civilians, agricultural land and the longer-term return of residents to their homes and livelihoods near the Blue Line.

“This is not the first time that the IDF has dropped unknown chemical substances from airplanes over Lebanon,” the mission said, reiterating its call on the IDF “to stop all such activities and work with peacekeepers to support the stability we are all working to achieve.”