Israeli officials said Iran would pay a price for the strike.

The missile attack came after Israel said ground troops crossed into Lebanon, while Hezbollah said it saw no sign of Israeli forces and that its troops were ready to confront them.

Israel said its incursion would be focused on the narrow strip of land just across the border. But it also issued evacuation warnings covering a wider swath of Lebanon, raising fears that a large-scale ground invasion was soon to come.

In recent days, a wave of Israeli airstrikes has killed Hezbollah leader Hassan Nasrallah and several of his top commanders, while driving hundreds of thousands of Lebanese from their homes.

Israel claims a ground operation is now necessary to return tens of thousands of displaced Israelis to their homes in the north, pummeled by continuous rocket fire from Hezbollah since Oct. 8.

Here's what we know:

Why did Iran launch missiles toward Israel?
 

Israel's army said it identified 180 missiles launched from Iran shortly after 7:30 p.m. Sirens blared across the country, and Israelis were ordered to stay in protected areas. An Israeli security official said that in cooperation with the United States, the Israeli Air Force intercepted many of the missiles, though there were some direct hits damaging buildings and igniting some fires.

Iran state TV said Teheran fired 200 missiles at Israel including hypersonic weapons for the first time, 

U.S. and British officials later said approximately 200 missiles had been launched by Iran.

Iran said the missiles were in response to the assassination of Hezbollah leader Hassan Nasrallah and Revolutionary Guard Gen. Abbas Nilforushan, both killed in an Israeli airstrike last week in Beirut. It also mentioned Ismail Haniyeh, a top leader in Hamas who was assassinated in Tehran in July. It warned this attack represented only a “first wave,” without elaborating.

In April, Iran launched more than 300 drones, ballistic missiles and cruise missiles at Israel in retaliation to Israel attack on its consulate in Syria. Most were intercepted outside of Israel. Israel vowed to respond, pushing the two archenemies closer toward confrontation and the region closer toward a broader war.

What kind of missiles did Iran use in the attack?
 

Iranian state media described the country as using several types of ballistic missiles in its attack on Israel. Among them were the the Emad and Ghadr, as well as Iran’s new Fattah missile.

Officials last year claimed the Fattah, or “Conqueror” in Farsi, travelled as fast as 15 times the speed of sound with a range of up to 1,400 kilometres (870 miles). Tuesday’s attack marked the first time Iran’s Revolutionary Guard has claimed firing the Fattah missiles in anger.

However, questions remain over just how manoeuvrable the missile is as it comes back into the atmosphere to strike a target. The more irregular the missile’s flight path, the more difficult it becomes to intercept. Missile experts who analyzed footage of remains of missiles recovered after the attack suggested the Fattah had been used.

Did Israeli troops enter Lebanon?
 

The army says that Israeli troops entered Lebanon late Monday, though it was not clear whether they remained inside or were moving in and out of the country.

In a surprise announcement, Israel said Tuesday that its ground forces have been operating covertly in Lebanon for the last year, carrying out dozens of small ground operations. Daniel Hagari, the army's spokesman, said the current raid is an expansion of these activities.

The Lebanese army and UNIFIL, a U.N. peacekeeping force stationed in southern Lebanon, have not confirmed that Israeli troops crossed the border, although UNIFIL said it was notified that they were going to.

How far into Lebanon are Israeli ground troops?
 

An Israeli army official, speaking on condition of anonymity under briefing guidelines, said Israeli ground troops were “within walking distance” of the border, targeting the small Lebanese villages hundreds of meters (yards) from Israeli territory.

The army says Hezbollah militants remain in the area, despite heavy Israeli bombardment over the past few weeks.

Have there been clashes between Hezbollah and Israeli troops?
 

There were no signs of ground combat in southern Lebanon, and the Israeli official said there had been no clashes with Hezbollah.

Meanwhile, the cross-border fire continued. Hezbollah said it had targeted groups of soldiers in several Israeli border areas with artillery shelling and rockets. Israel said no soldiers were injured. At the same time, Israeli artillery units pummeled targets in southern Lebanon and the sounds of airstrikes were heard throughout Beirut.

Hezbollah retaliated firing a rare volley of rockets toward central Israel on Tuesday, injuring one man, Israeli paramedics said.

How extensive is the planned operation?
 

Israel has not given a timetable for how long the incursion will last and has declined to specify how far troops will go.

The army official said that marching to Beirut, as Israel did in its 1982 invasion of Lebanon, is “not on the table.” At the time, the Israeli invasion was also pitched as a limited incursion to push the Palestine Liberation Organization back.

He added that the operation in its current stages does not mirror Israel’s ground incursions in Gaza, where the army entered cities with heavy manpower, artillery and tanks.

That could change, depending on whether Israel’s government decides to launch a more extensive ground operation. Large numbers of forces, including scores of tanks, have massed along the border in recent days.

Israeli troops that entered Lebanon are from the 98th division, the army said. The division is responsible for some of the heaviest fighting inside Gaza and includes elite units specializing in attacks behind enemy lines.

Meanwhile, Israel is expanding its evacuation warnings in southern Lebanon, sending hundreds of thousands of Lebanese fleeing from the south.

On Tuesday, itnasked residents living in villages north of a U.N.-declared buffer zone to flee. Under a U.N. resolution that ended the 2006 war, the zone was supposed to be controlled by a U.N. peacekeeping force and the Lebanese military.

* This story was edited by Ahram Online.