This morning's exchange of strikes between Israel and Hezbollah appears to be a significant escalation.
The Israeli military says around 100 fighter jets carried out what it described as pre-emptive strikes on Hezbollah targets across southern Lebanon on Sunday morning. Hezbollah later fired rockets and missiles into northern Israel.
If that 100 figure is correct, it would be the largest Israeli attack on Lebanon since the full-scale war between Israel and Hezbollah in 2006.
Israel's strikes happened at around 04:30 local time (01:30 GMT), and it said that Hezbollah was planning a large-scale attack half an hour later, at 05:00 local time.
According to reporting by the New York Times, quoting an anonymous Israeli intelligence official, this included rocket strikes on Tel Aviv, the country’s biggest city, deep inside central Israel.
In the end Hezbollah said it had fired more than 300 rockets and missiles targeting military facilities in northern Israel, where air raid sirens have been sounding.
Across the region, the fear is this latest escalation could once again lead to all-out war.
In a statement, Hezbollah said this was the first phase of its response to the Israeli assassination of a senior commander Fouad Shukr in a strike in Beirut on 30 July.
It is widely believed Israel was behind the assassination of the political leader of Hamas, Ismail Haniyeh, in a strike in the Iranian capital Tehran the following day.
Ever since, the region has been waiting for a response from both Hezbollah and Iran.
From Iran, it is yet to come.
But this appears to be Hezbollah’s first significant retaliation.
For weeks now diplomats have been working to try to avoid the crisis in Gaza escalating into a wider regional conflict.
The United States has warned the ongoing failure to agree a ceasefire and hostage release deal between Israel and Hamas could see those diplomatic efforts fail.
But despite intense US pressure, talks to establish a ceasefire deal for Gaza after more than 10 months of war have led to nothing.
Israel’s military says it is ready to fight a war on two fronts: in Gaza and on its northern border with Lebanon.
But Hezbollah is a far more formidable force than Hamas.
It’s estimated it has around 150,000 rockets, some capable of reaching targets across Israel.
Its fighters, some of whom have fought in the war in Syria, are well trained and better equipped than those of Hamas.
Almost a year into the conflict in Gaza, some question whether there is appetite in Israel for another war.
Hundreds of thousands of Israeli army reservists have been called up to fight in Gaza, often serving several tours.
But many Israelis, especially those from the north, say Hezbollah needs to be dealt with.
Tens of thousands of people living there have been evacuated from their homes since the start of the war in Gaza. Many have lost their businesses.
In southern Lebanon too, tens of thousands of people have been forced to leave their homes because of fears of Israeli strikes.
What happens next?
Hezbollah, for now, has said it has concluded the first phase of its retaliation for the killing of Fouad Shukr.
Its strikes on Israel this morning appear to have caused relatively little damage and there have been few casualties on either side.
Israel believes it successfully thwarted a major Hezbollah attack.
The question becomes: will we now see a return to the more routine cross-border "tit for tat" that has been going on since the start of the war in Gaza last October?
Or could today's violence escalate into something far more dangerous?
Israeli and Hezbollah leaders say they do not want another full-scale war. But both sides say they are ready for it.
Source: BBC
