Hezbollah leader Sayyed Hassan Nasrallah on Sunday warned the Israeli army stationed along the border with Lebanon that his movement was preparing an imminent response to two Israeli drones which crashed overnight in a suburb of Beirut.
Nasrallah, whose Iran-backed movement fought a one-month war with Israel in 2006, issued the toughest warnings to his enemy in years.
"We are in a new stage," Nasrallah said in a televised speech, referring to the group's long enmity with Israel.
He said the "suicide drone" attack was intended for a specific target and was a "very, very, very dangerous development" and that everything possible would be done to prevent a repeat.
Nasrallah's comments also followed overnight strikes claimed by Israel that he said killed two Lebanese Hezbollah fighters in Syria.
In the first such incident in more than a decade, one drone fell and second exploded before dawn near the ground and caused some damage to Hezbollah's media centre in the southern suburbs of the capital which it dominates, a Hezbollah official told Reuters.
Nasrallah said it marked "the first clear, big, dangerous, breach of the rules of engagement drawn up in 2006" after the end of the 2006 conflict between Israel and Hezbollah.
"If we keep quiet on this violation, this will lay a dangerous path for Lebanon," he said, adding that unstopped drone attacks could lead to a situation similar to what is happening in Iraq.
The Iran Militia in Iraq and Syria (IMIS), a grouping of Iraq's mostly Shi'ite Muslim paramilitary groups, many of which are backed by Iran, on Wednesday blamed recent blasts at their weapons depots and bases on the United States and Israel.
Israeli Prime Minister Benjamin Netanyahu has hinted of possible Israeli involvement in attacks against Iran-linked targets in Iraq.
"We will not allow the clock to be turned back, we will not allow Lebanon to be violated by bombardment, killing or explosions...This for us is a red line," said Nasrallah.
Although Israel has not claimed the Beirut attack, Nasrallah said it was the first Israeli attack inside Lebanon since 2006.
Lebanese Prime Minister Saad Hariri said the drones aimed to stir up regional tensions.
The Israeli military declined to comment.