The United Nations peacekeeping mission said three United Nations observers and an interpreter were injured in shelling in Rumeish, southern Lebanon.
Lebanese state news agency reported that an Israeli drone strike was behind the explosion, but the Israeli military denied responsibility.
UN investigators UNIFIL said the injured were being treated and the cause of the explosion was being investigated.
This comes in the wake of rising tensions along the unofficial border between Israel and Lebanon.
Unifil said in a statement that an artillery shell exploded near the group, which was on foot patrol along the United Nations Blue Line dividing southern Lebanon and Israel.
He said targeting peacekeepers was “unacceptable”.
No details were given about the nationality or condition of the guards. The Lebanese interpreter is reported to be stable.
Lebanon's state news agency said Israeli “enemy drones” struck an area in southern Lebanon, injuring observers.
The Israeli military denied this, saying in a statement: “Contrary to reports, the Israel Defense Forces [Israel Defense Forces] There was no collision with a UNIFIL vehicle in the Rumeish area this morning. ”
In recent days, tensions have flared up again along the unofficial border between Israel and Lebanon, resulting in casualties on both sides.
Israel and the armed group Hezbollah carry out near-daily cross-border attacks, which began with the start of the Israel-Gaza war following Hamas' attack on Israel on October 7.
Hezbollah is a Lebanese Shiite Islamic extremist group with close ties to Iran and an ally of Hamas.
On Friday, Israeli Defense Minister Yoav Gallant said the Israel Defense Forces would step up attacks against the group in Lebanon and “move from defeating Hezbollah to actively pursuing it.”
“Wherever they are hiding, we will get to them,” he said.