Lebanon's premier condemned Tuesday a "dangerous military escalation" by Israel after a security incident at the border led the Jewish state to fire artillery across the frontier.
"Israel has once again violated Lebanon's sovereignty... in a dangerous military escalation," Hassan Diab said on Twitter, in his government's first official response to Monday's shelling.
"I call for caution in the coming days because I fear that things will get worse in light of severe tension at the border," he added.
The Israeli army had said a group of three to five men armed with rifles crossed the UN-demarcated Blue Line in the disputed Mount Dov area, claimed by Lebanon, Syria and Israel.
It said the "terrorists" had fled back to Lebanon after an exchange of gunfire and that Israeli forces had fired artillery into Lebanon "for defensive purposes".
Israel blamed the Lebanese Shiite militant group Hezbollah for the infiltration attempt and on Tuesday its prime minister, Benjamin Netanyahu, said it had been acting on behalf of Iran.
"Everything happening now is the result of the effort by Iran and its Lebanese proxies to entrench militarily in our region," he said during a visit to the Israeli army's northern command headquarters.
"We will continue to take action to thwart Iran's military entrenchment in our region," he added. "We will do whatever is necessary to defend ourselves and I suggest that Hezbollah consider this simple fact. Israel is ready for any scenario."
But Hezbollah, which has a presence in the area where Monday's incident occurred, denied any involvement.
It said that reports of Israel thwarting an infiltration from Lebanon are "completely false."
- UN peacekeeping mandate -
United Nations peacekeeping force UNIFIL said it had opened an investigation into the incident.
Diab on Tuesday accused Israel of trying to "change the rules of engagement," that have existed between the two countries since the end of a month-long 2006 war -- the last direct conflict between the two states.
He also said that Lebanon rejects a push by Israel to alter the mandate of UNIFIL before it expires late next month.
"There is an attempt to pressure Lebanon by threatening to reduce the number of UNIFIL forces if the mission's mandate is not changed," Diab said.
"Lebanon refuses to amend the tasks of UNIFIL."
In early May, the US ambassador to the UN, Kelly Craft, called on the world body to "pursue serious change to empower UNIFIL or realign its staffing and resources," because the mission was being "prevented from fulfilling its mandate."
Hezbollah chief Hassan Nasrallah swiftly rejected the proposal which he said was an Israeli demand.
Commenting on Monday's events, President Michel Aoun said it threatened stability in south Lebanon weeks ahead of UNIFIL's mandate renewal.
The latest border incident follows a July 20 Israeli missile attack on Syrian government and allied positions south of Damascus that killed five people.
Hezbollah, whose fighters back Damascus in the nine-year-old Syrian civil war, said one of its own was among the dead.
Since 2011, Israel has launched hundreds of strikes in Syria, targeting government troops and allied Iranian and Hezbollah forces with the stated aim of ending Iran's military presence in Syria.
Israeli has deployed more armoured vehicles and artillery to the Lebanese border prompting Lebanon's Prime Minister Hassan Diab to accuse it of a "dangerous" escalation
Lebanese Prime Minister Hassan Diab accused Israel of seeking to alter the mandate of the UN peacekeeping force that has been monitored the border since 1978 before it expires late next month