United Nations peacekeepers said three military observers and a translator were wounded Saturday in a blast in southern Lebanon, where Israel and the Hezbollah movement trade frequent cross-border fire.

Peacekeepers from the United Nations Interim Force in Lebanon (UNIFIL) patrol the so-called Blue Line, the border demarcated by the UN in 2000 when Israeli troops pulled out of southern Lebanon.

The UN Truce Supervision Organization (UNTSO) supports the peacekeeping mission.

Three UNTSO "military observers and one Lebanese language assistant on a foot patrol along the Blue Line were injured when an explosion occurred near their location", UNIFIL spokesperson Andrea Tenenti said in a statement.

The wounded were "evacuated for medical treatment" and UNIFIL is "investigating the origin of the explosion", Tenenti added.

"Safety and security of UN personnel must be guaranteed," the statement said, urging "all actors to cease the current heavy exchanges of fire before more people are unnecessarily hurt".

Israel and Lebanon's Iran-backed Hezbollah movement have exchanged near-daily fire since Palestinian militant group Hamas carried out an unprecedented attack on southern Israel on October 7, triggering war in Gaza.

Hezbollah, which has a powerful arsenal of rockets and missiles, says its attacks on Israel are in support of Hamas.

UN chief Antonio Guterres "condemns" the Saturday blast and underscored "grave concern" over the frequent exchange of fire along the Blue Line, spokesman Stephane Dujarric said in a statement.

Norway's defence ministry said a Norwegian UN observer was "lightly injured" and had been admitted to hospital.

"The circumstances surrounding the attack are unclear," defence ministry spokesperson Hanne Olafsen told Norwegian news agency NTB.

UNIFIL's Tenenti told AFP that the other two observers were from Australia and Chile, adding that all four wounded were in "stable" condition.

- 'Dangerous incident' -

Lebanon's state-run National News Agency said an "enemy (Israeli) drone" raided the Rmeish area of southern Lebanon where the UNTSO observers were wounded.

The Israeli army told AFP in a statement: "We did not strike in the area."

Tenenti emphasised: "All actors have a responsibility under international humanitarian law to ensure protection to non-combatants, including peacekeepers, journalists, medical personnel and civilians."

Lebanese Prime Minister Najib Mikati condemned what he called a "dangerous incident".

Lebanon's foreign ministry said the attack was "in violation of international law".

Cross-border fire since October has killed at least 347 people in Lebanon, mostly Hezbollah fighters, but also at least 68 civilians, according to an AFP tally.

The fighting has displaced tens of thousands of people in southern Lebanon and in northern Israel, where the military says 10 soldiers and eight civilians have been killed.

An uptick in deadly exchanges in recent days has fuelled concerns of an all-out conflict between Israel and Hezbollah, who last fought a war in 2006.

UNTSO was set up after the 1948 war that accompanied Israel's creation to monitor armistice agreements reached with its Arab neighbours.

It also assists other UN peacekeeping operations in the region, including UNIFIL, which was established after Israel's 1978 invasion of south Lebanon and expanded following the 2006 war.