The Israeli army said the bombardment in the early hours of Friday was in response to a barrage of rockets fired by Hamas in Lebanon the previous day. Separately, it launched air attacks overnight on the besieged Gaza Strip, which is run by Hamas.

The firing of rockets come after Israeli police attacked Palestinians worshippers inside Jerusalem’s Al-Aqsa Mosque for the second night in a row this week.

Here’s what you need to know.

What happened?

The Israeli military tweeted on Thursday that 34 rockets had been fired from Lebanon, with 25 intercepted, and at least four landing in Israel. It was the first rockets fired from Lebanon towards Israel since last April and the biggest launch since Israel and Lebanon’s powerful Shia movement Hezbollah fought a war in 2006.

Medics in Israel said three people were injured in the rocket fire, including a 19-year-old man with shrapnel injuries in mild condition and a 60-year-old woman injured while running to a nearby shelter. Several others were treated for shock.

Israel’s army announced in a short statement at 4:07am (01:07 GMT) on Friday that it “is currently striking in Lebanon”. A Lebanese TV station reported explosions near a Palestinian refugee camp in the southern port city of Tyre.

No casualties were reported and most missiles fell in open spaces.

The Lebanese government said its troops and United Nations peacekeepers had launched an investigation to find the perpetrators.

On Friday, the Lebanese army said in a statement it had located a rocket launcher, including several rockets, in the town of Marjaajoun, near the Israeli border.

Who fired the rockets?

There was no immediate claim of responsibility for the rocket fire, which came amid assaults by Israeli forces on Palestinian worshippers at Al-Aqsa this week that led to regional and global condemnation of Israel.

The Israeli army said it believed the rocket fire was “a Palestinian-oriented event”, connecting to the violence in Jerusalem.

Israeli military spokesman Richard Hecht said either Hamas or Palestinian Islamic Jihad, both of which are based in Gaza but also operate in Lebanon, could be involved. He added the army believed that Hezbollah and the Lebanese government were aware of what happened and also held responsibility.

Separately, another army spokesman, Avichay Adraee, wrote on Twitter, “We are investigating the possibility of Iran’s involvement in the rocket fire from Lebanon,” Adraee added on Twitter.

Both Hamas and Hezbollah are Iranian allies and recently announced a joint operations room.

But Hamas representative in Lebanon Ahmed Abdel Hadi told Lebanese An-Nahar newspaper the group does not have “any information concerning the rockets” that were launched towards Israel.

“Security sources say Palestinian groups – many of which are armed and confined to camps – were behind the incident,” Al Jazeera’s Zeina Khodr reported from Tyre.

“Some analysts say they couldn’t have acted without the knowledge and backing of Hezbollah,” she said, noting that the Lebanese group “holds sway” in the country’s south.

Mohanad Hage Ali, of the Carnegie Middle East Center, told Al Jazeera that over the past few years “a large number of Hamas officials and representatives show up in Lebanon and also to a certain extent [have] Beirut as a base for their presence”.

Al Jazeera reached out to several Hamas officials in the Gaza Strip and Lebanon, as well as to the Palestinian Islamic Jihad group, but it was not possible to get a comment.

A Lebanese security official, who spoke to The Associated Press news agency on the condition of anonymity because he was not authorised to speak to media, said the country’s security forces believed the rockets were launched by a Lebanon-based Palestinian armed group, not by Hezbollah.

Could it be about something else?

The escalation came after Israel, in recent weeks, stepped up its aerial attacks against Iranian targets in neighbouring Syria.

The Iranian government, in a rare acknowledgement, said last week two of its military advisers were killed in an Israeli attack near Damascus and said it reserved the right to respond at an appropriate time.

There have also been other incidents recently that have heightened tensions, including the alleged infiltration of an armed man suspected of entering Israel from Lebanon last month and blowing up a car at a junction, according to the Israeli army.

What has the reaction been?

Hezbollah has not condemned the rocket fire. Its deputy leader, Sheikh Naim Qassem, said in a Twitter post the group was “vigilant” after Thursday’s exchange of fire over the Lebanon-Israel border.

But caretaker Lebanese Prime Minister Najib Mikati warned against Lebanon’s territory being used for acts that could threaten security in the country.

“Lebanon absolutely rejects any military escalation emanating from its land, and the use of Lebanese territory to carry out operations that may destabilise the existing stability,” Mikati said.

Israeli Prime Minister Benjamin Netanyahu pledged a tough response.

“We will strike our enemies and they will pay the price for any act of aggression,” he said at the start of a security cabinet meeting in Jerusalem on Thursday evening.

Iran, meanwhile, condemned the Israeli attacks in Lebanon and Gaza and called for action by international bodies, according to state media.

Iranian foreign ministry spokesman Nasser Kanaani said the ministry “strongly condemned the attacks … as a violation of Lebanon’s sovereignty and territorial integrity and a gross violation of international law and human rights of the oppressed Palestinian nation, and called for an effective response by … world bodies”, state media said.