Israel launched its Northern Arrows offensive across Lebanon on Sept 23, targeting Hezbollah strongholds in the south and the Bekaa Valley to the east in large-scale air strikes.

The major aerial bombardment came days after thousands of pagers and walkie-talkies belonging to Hezbollah fighters exploded simultaneously in dual attacks blamed on Israel, killing dozens and injuring 2,800.

Hezbollah has responded by firing hundreds of rockets into northern Israel, while a ballistic missile appeared to reach Tel Aviv for the first time before it was intercepted.

Israel’s army chief warned on Sept 25 it was preparing for a possible invasion of Lebanon, while Benjamin Netanyahu, the prime minister, dismissed calls from world leaders for a ceasefire, vowing to fight on with “full force”.

Here we explain why Israel might invade Lebanon, and the wider context of its conflict with Hezbollah.

Why is Israel at war with Hezbollah?

On Oct 8, previous sporadic fighting escalated when Hezbollah fired guided rockets and artillery at Israeli-controlled territory. The group said this was done in solidarity with Palestinians after the previous day’s Hamas-led assault on southern Israel that killed 1,200.

Israel evacuated 60,000 people living near the Lebanon-Israel border early on in the war, and has traded near-daily cross-border fire with Hezbollah ever since.

Tensions have recently spiralled into the risk of all-out war because of Israel’s widespread air strikes across Lebanon, the pager attacks and Israel’s killings of senior Hezbollah commanders in Beirut’s southern suburbs.

Why might Israel invade Lebanon?

Lt Gen Herzi Halevi, Israel’s army chief, told IDF troops their “boots will enter enemy territory” after three days of bombings across Lebanon under Operation Northern Arrows.

His statements, paired with the activation of 4,000 reservists to be sent to the northern front, is a signal that Israel intends to escalate its offensive.

Joe Biden, the US president, said on Sept 25 that an all-out war was possible but not “inevitable”, while Sir Keir Starmer urged all British citizens to leave Lebanon immediately, saying the situation was deteriorating “hour on hour”.

What happens next?

Israel could launch a full-scale invasion of Lebanon to remove what remains of Hezbollah from its bastions in the southern villages, the Bekaa Valley and the southern suburbs of Beirut.

It could also launch a limited invasion with the intent to create a buffer zone. Senior Israeli military figures have suggested occupying the area between the Lebanon-Israel border and the Litani River.

Tensions could also de-escalate. Although the death toll in Lebanon has been the highest since the 2006 Hezbollah-Israel war, the Iran-backed group has yet to use its most devastating missiles, which suggests that Iran could be restraining the group. Tehran has also reportedly rejected requests from Hezbollah to join the fight with a direct attack on Israel.

Who was behind the pager attacks?

Israel has rejected claims that it was behind the clandestine operation to plant explosives in Hezbollah pagers and walkie-talkies, but experts widely believe that Mossad, Israel’s national intelligence agency, was responsible.

Hezbollah officials have described the attack as the most serious security breach in the history of the group, and said it dealt a severe blow to its logistics. The blasts took at least 1,500 members of its fighting force out of action, most blinded or maimed.

Israel is already strongly suspected of being behind the killing of Ismail Haniyeh, the Hamas political chief who was assassinated in Tehran on July 31 shortly after meeting Iranian officials.

Israel generally has a policy of not commenting on attacks or assassinations carried out overseas, though its leaders do sometimes allude to them.

What is Hezbollah?

Hezbollah is a radical Shia Islamist paramilitary group based in Lebanon.

Backed by Iran, it is considered to be the most powerful and heavily armed non-state actor in the world.

Its leader, Hassan Nasrallah, has claimed that the group could field more than 100,000 trained fighters, although independent observers believe that this is more likely to be 20,000 to 50,000.

Hezbollah is stronger than the cash-strapped Lebanese military, which has been reduced to selling tourist rides in its ageing fleet of 1960s helicopters. Lebanese soldiers also often take on second jobs to supplement their meagre $100-a-month salary.

The terror group boasts a fearsome long-range armoury, which ranges from cheap Katyusha rocket artillery to high-tech Fateh 110 precision-guided ballistic missiles.

Where did Hezbollah come from?

After Israel invaded Lebanon in 1982, forcing its long-term enemy the Palestine Liberation Organization to flee to Tunisia, it kept troops stationed in a southern buffer zone.

Disparate Islamist militias that continued to fight Israeli troops subsequently consolidated under an Iran-backed initiative that was to become Hezbollah.

The group pioneered modern terrorist tactics, such as suicide bombings and kidnappings, and fought against peacekeepers and international actors.

In 1983, it bombed the US embassy in Beirut, killing 63 people.

In 1985, it published a manifesto in which it pledged the destruction of Israel.

Hezbollah continued to fight against Israeli troops stationed in Lebanon until Israeli forces withdrew on May 25, 2000 – a day that is now a Lebanese public holiday.

In 2006, a full-blown war broke out between Hezbollah and Israel, sparked by a deadly cross-border raid by the Iran-backed terror group.

In what became known as the Second Lebanon War, Israeli troops invaded southern Lebanon, leading to a 34-day conflict that killed 1,000 civilians. Both Hezbollah and Israel claimed victory.

What are the differences between Hezbollah and Hamas?

Hamas and Hezbollah are both Islamist groups committed to the destruction of Israel, but there are key differences between them.

Hamas, a Palestinian organisation, is a Sunni offshoot of the Muslim Brotherhood. It has ruled the Gaza Strip since 2007 after it defeated rival group Fatah in an election, and in subsequent violent clashes.

Hezbollah is a Lebanese Shia group that was formed by Iran during the Lebanese Civil War to fight Israel.