The slaying of Hamas deputy leader Saleh al-Arouri in an alleged Israeli drone strike in Beirut on Tuesday has brought the Lebanese branch of the Palestinian terror group into the spotlight.

Hundreds attended Arouri’s burial on Thursday at the Sabra and Shatila Martyrs’ Cemetery, in the refugee camp whose residents were massacred in 1982 by Israeli-backed Lebanese Christian Phalangists.

Lebanon is notoriously home to the terror group Hezbollah, another arch-enemy of Israel backed by Iran. Since at least 2018, Hamas has quietly cooperated with Hezbollah on establishing a Lebanese branch to open up an additional front against Israel during conflicts. Arouri was the key architect of that rapprochement.

For years, Hamas leaders have attempted to escape targeted killings by Israel by finding shelter in countries that support the group – most prominently Qatar, Lebanon and Turkey, but also Iran and Malaysia.

Of those host countries, Lebanon is the only one sharing a border with Israel. It is also home to 12 camps hosting tens of thousands of Palestinian refugees and their descendants. By longstanding agreement, the Lebanese army does not enter the camps, leaving security inside them to Palestinian factions, including Hamas, which allows the terror group to recruit new members undisturbed.

In 2018, it became public that Israel had repeatedly appealed to the United Nations to prevent Hamas from entrenching itself in southern Lebanon, alongside Hezbollah, charging that the cooperation between the two Iran-backed organizations was a “blatant violation” of UN Security Council Resolution 1701, which ended the 2006 Second Lebanon War between the Israeli military and Hezbollah.

In a letter by Israel’s then-ambassador to the United Nations, Danny Danon, Israel said that Hamas had been receiving Hezbollah’s assistance to establish missile factories and camps to train thousands of Palestinian terrorists in southern Lebanon.

The Hamas branch was reportedly first established in the coastal city of Tyre, but opened other outposts throughout the country.

Danon’s letter, dated May 11, 2018, stated: “The increasing cooperation between Hamas, Hezbollah and Iran constitutes a major threat not only to Israel but to the stability and security of the entire region.” The letter explicitly cited Arouri, the deputy leader of Hamas who was liquidated on Tuesday, as the man responsible for that coordination.

After spending 18 years in Israeli prisons for his role in planning Hamas attacks in the West Bank, Arouri was released in 2010. He initially moved to Syria, and later to Turkey.

He was based in Istanbul until 2015, when he was placed on a US most wanted list, after he admitted to being one of the masterminds of the kidnapping and killing of three Israeli teens in the West Bank that sparked the 2014 Gaza war.

When Turkey and Israel initiated a rapprochement in 2016 and Turkey expelled members of various Islamist groups, Arouri began to shuttle between Istanbul and Beirut and started working on building the infrastructure for Hamas in Lebanon with Hezbollah and Iranian support.

Hamas and Hezbollah were not always allies: The two terror movements went through a turbulent patch during the Syrian civil war that erupted in 2011 when Hamas supported the Syrian opposition while Hezbollah backed the regime of Bashar al-Assad. The two groups reportedly faced off in Yarmouk and other Palestinian refugee camps in Syria.

As the Syrian conflict gradually subsided, and with the election of Ismail Haniyeh as leader of the Hamas politburo in 2017, the Palestinian group began gravitating towards Iran and realigned itself with Hezbollah.

The main architect of the rapprochement was Arouri, who then emerged as the focal point for laying down Hamas’s infrastructure in Lebanon.

In the summer of 2018, Arouri took residence in Beirut, in the southern Shi’ite neighborhood of al-Dahiya, which serves as Hezbollah’s stronghold. He was soon followed by Khalil al-Hayya, leader of Hamas’s Arab and Islamic relations, and Zaher Jabarin, in charge of Palestinian prisoners in Israeli jails.

In May 2021, Lebanese media reported that Hezbollah and Hamas had set up a joint operations room in Beirut with the coordination of Iran’s Islamic Revolutionary Guards Corps (IRGC), which had sent weapons and ammunition to Gaza during the 11-day conflict between Israel and Hamas in May 2021, and “moved a number of Palestinian resistance officers out of the Strip during the aggression.”

The head of Hamas’s military wing, Yahya Sinwar, confirmed that the terror group had coordinated with the IRGC and Hezbollah throughout the fighting, according to Hebrew media.

On April 6, 2023, Hamas launched a massive rocket attack against Israel from Lebanon, with at least 36 projectiles fired across Israel’s northern border, many of which were intercepted by the Iron Dome air defense system. It was the heaviest rocket barrage since the 2006 Second Lebanon War.

The attack gave a first glimpse into the military capabilities of the Palestinian terror group’s foreign branch. Hamas’s arsenal appeared to include Grad-type rockets of Iranian production, which an expert described to The Times of Israel as “basic, simple and inaccurate,” fired from makeshift launchers.

Hezbollah has similar equipment in its arsenal, suggesting that it may have handed over some of its missiles to Hamas.

In August 2023, Prime Minister Benjamin Netanyahu threatened to assassinate senior Hamas figures, including Arouri, in light of an escalation in the West Bank.

In response, Hamas issued an official statement stressing that the Israeli prime minister’s threats would not succeed in weakening the “resistance,” and Arouri said that the move could spark a “regional war.”

Following the Hamas announcement, photos appeared on social media of Arouri talking on the phone in his office, dressed in military uniform and with an M-16 rifle on his desk, in a show of defiance at Israel.

On September 2, a few weeks before Hamas’s shock onslaught of October 7, Arouri accompanied a Hamas delegation led by politburo chief Haniyeh in a meeting with Hezbollah leader Hassan Nasrallah and Palestinian Islamic Jihad leader Ziyad Nakhaleh, in which the issue of cooperation along the “axis of resistance” was discussed, as well as “the intensification of resistance in the West Bank and Gaza.”

Along with Arouri, two other Hamas military commanders were slain on Tuesday: Samir Findi and Azzam Al-Aqraa, along with Hamas figures Mahmoud Shaheen, Muhammad Bashasha, Muhammad al-Rayes and Ahmed Hammoud.

According to Hebrew media reports, Findi, 54, had been a Hamas member for 30 years and was the de facto commander of the group’s military wing in Lebanon, as well as the liaison with the Houthi rebels in Yemen.

Al-Aqraa reportedly coordinated terror attacks in the West Bank while living in Syria, Saudi Arabia and Turkey.