Israeli and Lebanese troops exchanged fire on their often tense border on Monday morning, officials on both sides said, with the two armies trading accusations on why the shooting incident occurred.
The Israeli military said its troops had been fired upon as they worked on the Israeli side of the Blue Line, the UN-drawn border with Lebanon.
But a Lebanese army official said troops opened fire only when Israeli soldiers crossed the border line, which was established in 2000.
Both sides have challenged the accuracy of the Blue Line in several locations.
"Earlier this morning an IDF (Israeli military) force carrying out a routine patrol within Israeli territory near the Israel-Lebanon border was fired upon from the direction of Lebanon," an Israeli military spokeswoman told AFP.
"The force responded by firing towards the source of fire and UNIFIL was informed of the incident," she added, referring to the UN peacekeeping force stationed on the Israeli-Lebanese border.
One Israeli military source said the incident occurred near the Dan kibbutz in the far north of Israel as troops carried out work on a border fence.
Another stressed that "Israel's interest at this time is to contain the situation and maintain the calm on the border."
A Lebanese army official, who declined to be identified, said the incident occurred early on Monday when "an Israeli patrol in the Wazzani area crossed the Blue Line and went beyond it about 30 metres (yards)."
"Lebanese troops stationed in the area fired warning shots," he said. "The Israeli patrol retreated and then fired at Lebanese army posts."
He said there were no injuries on the Lebanese side and that UNIFIL was informed of the incident and quickly moved to the area.
UNIFIL spokesman Neeraj Singh confirmed that the incident had occurred, but gave no details on whether Israeli troops had crossed the Blue Line.
"We can confirm that at around 7:00 am this morning there was a brief exchange of fire between the Lebanese army and the Israeli army along the Blue Line in the general area of Wazzani," Singh said.
"UNIFIL peacekeepers immediately responded to the location in order to contain the situation and prevent any escalation. The firing has since ceased and the situation in the area is quiet. No casualties have been reported."
Singh said UNIFIL had opened an investigation into the shooting.
Monday's incident, which came as Lebanon marks Army Day, came almost exactly a year after Lebanese and Israeli troops traded fire along the tense border, leaving two Lebanese soldiers and a journalist killed along with a senior Israeli officer.
The flare-up in violence was the worst clash between the two sides since Israel's devastating 2006 war in Lebanon against the Shiite Hezbollah militia.