Israel's military said its jets preemptively struck thousands of Hezbollah rocket launchers across southern Lebanon on Sunday after identifying that Hezbollah was preparing an imminent attack on Israel.

Hezbollah has said it then launched hundreds of rockets and drones at Israel in an initial response to the killing of a top commander last month, and denied its plans had been thwarted.

It was a significant escalation after 10 months of almost daily exchanges of fire along the Israel-Lebanon border, which have raised fears of an all-out war between the two enemies.

What is Hezbollah?

Hezbollah is a Shiite Muslim organization that wields political influence and controls the most powerful armed force in Lebanon.

It was created in the early 1980s by the most dominant Shiite power in the region, Iran, to oppose Israel. At the time, Israeli forces had occupied southern Lebanon during the country's civil war.

Hezbollah has participated in national elections since 1992 and has become a major political presence.

Its armed wing has carried out deadly attacks on Israeli and American forces in Lebanon. When Israeli troops withdrew from Lebanon in 2000, Hezbollah took credit for their departure.

Since then, Hezbollah has maintained thousands of fighters and a large arsenal of rockets in southern Lebanon. It continues to oppose Israel's presence in the disputed border areas.

It has been designated as a terrorist organization by Western countries, Israel, the Arab countries of the Gulf and the Arab League.

In 2006, full-scale war broke out between Hezbollah and Israel, triggered by a deadly cross-border attack by Hezbollah.

Israeli troops invaded southern Lebanon in an attempt to eliminate the threat from Hezbollah. However, she survived and has since increased her number of warriors and acquired new and better weapons.

Who is the leader of Hezbollah, Hassan Nasrallah?

Sheikh Hassan Nasrallah is a Shiite cleric who has led Hezbollah since 1992.

He played a key role in its transformation into a political as well as a military force.

He has close ties to Iran and its supreme leader, Ayatollah Ali Khamenei.

Nasrallah has not appeared in public for years, apparently out of fear of being killed by Israel.

However, he remains revered by Hezbollah and gives televised speeches every week.

How powerful are Hezbollah's forces?

Hezbollah is one of the most heavily armed non-state military forces in the world. It is financed and equipped by Iran.

Hassan Nasrallah has claimed to have 100,000 fighters, although independent estimates range between 20,000 and 50,000.

Many of them are well-trained and battle-experienced, having fought in the Syrian civil war.

Hezbollah has an estimated 120,000-200,000 missiles and rockets, according to the Center for Strategic and International Studies.

Most of its arsenal consists of small unguided surface-to-ground artillery missiles.

But it was also thought to have anti-aircraft and anti-ship missiles, as well as guided missiles capable of striking deep inside Israel.

This is far more sophisticated than what Hamas in the Gaza Strip has at its disposal.

Could Hezbollah go to war with Israel?

Earlier sporadic fighting escalated on October 8 - a day after an unprecedented attack on Israel by Hamas gunmen from Gaza - when Hezbollah fired on Israeli positions in solidarity with the Palestinians.

Since then, it has fired more than 8,000 rockets into northern Israel and Israeli positions in the Golan Heights, fired anti-tank missiles at armored vehicles and attacked military targets with explosive drones.

The Israel Defense Forces (IDF) have responded, using airstrikes and tank and artillery fire against Hezbollah positions in Lebanon.

Lebanon's health ministry says more than 560 people have been killed in the past 10 months. Most of them were Hezbollah fighters, but at least 133 were civilians, according to the ministry.

In Israel, authorities say at least 26 civilians and 23 soldiers have been killed.

Almost 200,000 people have also been displaced on both sides of the border.

Despite the fighting, observers say that so far both sides have aimed to contain hostilities without crossing the line into full-scale war. But there are fears that the situation could get out of control.

Those fears grew after 12 children were killed in a rocket attack on the Israeli-occupied Golan Heights on July 27. Israel said Hezbollah carried out the attack, but the group denied involvement.

On July 30, the IDF announced that it had killed Hezbollah's top military commander Fuad Shukr in an airstrike in the southern suburbs of Beirut.

A day later, the political leader of Hamas, Ismail Haniyeh, was killed in the Iranian capital, Tehran. Israel neither confirmed nor denied involvement.

Since then, the region has awaited a response from Hezbollah and Iran, both of which vowed to retaliate against Israel.

The US hopes to de-escalate tensions by brokering a ceasefire and hostage release deal in Gaza and is putting pressure on Israel and Hamas. Hezbollah has said that it will stop hostilities only after the fighting in Gaza ends./BBC/