BEIRUT – Hezbollah and the Syrian army launched a joint offensive against militant groups holed up in a rugged mountainous section of the Lebanese-Syrian frontier Friday, in a move that could have important repercussions for Lebanon’s vulnerable refugee population and Hezbollah’s supply lines in Syria.

A military media unit run by Hezbollah reported strikes against militant positions on the outskirts of the Lebanese border town of Arsal and areas near the Syrian town of Fleita on Friday and broadcast footage purporting to show artillery being fired at insurgent groups.

Some 3,000 militants, including al-Qaida-linked insurgents and members of the so-called Islamic State group, are said to be camped in the mountainous terrain outside the town of Arsal, which has been buffeted by the war in Syria since 2011.

The Syrian military has intensified its routine airstrikes on their side of the border over the past week, with residents in Arsal telling Syria Deeply that airstrikes were as close as “2 kilometers (1.2 miles) away” from refugee encampments.

The Lebanese army has also participated in the shelling of militants near Arsal this week. It has carried out strikes on militant positions on Lebanon’s side of the border, only days after Prime Minister Saad Hariri announced the start of an army operation to rid the area of extremist groups.

As the first strikes target the outskirts of Arsal, we look at what the offensive could mean for the 70,000 Syrian refugees in the area and Hezbollah as it returns to Lebanon’s northeastern battlefront for the first time in two months.

Arsal: a Key Frontier in the Syrian Conflict

Since August 2014, the Arsal outskirts has seen a strong presence of ISIS militants and former al-Qaida affiliate Jabhat Fatah al-Sham extremists in the mountainous territory since they jointly overran an army barracks in the border town. Lebanese police officers and soldiers were kidnapped. Many residents fled and remain internally displaced, and the army shelled the area as it tried to contain movement in and out of the town.

Nine soldiers are still held hostage by the so-called Islamic State.

It has since become a key border-crossing for ISIS and Jabhat Fatah al-Sham fighters between Lebanon and Syria, with at least five Arsal border crossings turning into flashpoints.

The consequences have been severe, most notably in late June 2016. Eight suicide bombings took place in a nearby Lebanese village of al-Qaa, killing five and wounding 30 in less than 24 hours. The interior ministry said that the militants crossed the eastern border into Lebanon prior to conducting the attacks.

Moreover, some 70,000 refugees are taking shelter in Arsal, where most take shelter in informal refugee settlements located not far from the border. These informal settlements are considered by UNHCR to be in among the “most vulnerable” localities in Lebanon’s northeast Baalbeck-Hermel region.

In November 2013, 6,000 Syrians from the town of Qarah fled into Arsal, according to the UNHCR, following increased Hezbollah presence and military operation in Syrian border towns. This added to the existing 20,000 registered by the U.N. agency.

A Prelude for Refugee Return?

With much of the Syrian frontier gradually secured under Hezbollah and Syrian government control since 2015, the Arsal battle could be the prelude to a large-scale refugee return. By clearing out the border area of militant groups, the Lebanese militia could push ahead with plans to establish so-called “safe zones” for refugees on the Syrian side of the border.

Hezbollah has previously called for safe zones near the border on the Syrian side for refugees to resettle in, which has caused speculation over the potential ease of transporting supplies through Iran.

Hezbollah has already started doing so through negotiating refugee returns and safe zones with Free Syria Army brigade Saraya Ahl al-Sham. Having negotiated since February among the 24 items in the negotiations include a refugee safe zone in the Qalamoun region in return for the latter militants to be exempt from punishment and conscription in the Syrian army. Two recent refugee returns to Damascus from Arsal have already taken place this month, one through a Hezbollah-mediated deal.

Though the United Nations has said that Syria is not yet safe for return, refugees around east Lebanon have crossed the border in large groups over the past few months, mostly to northeast Damascus suburb Asal al-Ward. The Lebanese army has reported that these are done voluntarily, most recently on June 10. The Hezbollah-affiliated War Media Center reported two groups of refugee families leaving to Asal al-Ward via Arsal two days later.

That being said, it’s not known whether these returns are voluntary or not, as they are reported after the families have crossed the border. Moreover, many Syrians have not returned, fearing war, imprisonment or forced conscription by the Syrian army.

Meanwhile, Lebanese politicians have recently prioritized Syrian refugee returns after five suicide attacks in late June wounded Lebanese soldiers during a raid on an informal settlement in Arsal. Lebanese politicians are divided over whether to enforce a refugee return policy in cooperation with the United Nations, or to coordinate directly with the Assad regime in Syria.

If Hezbollah and the Syrian army succeed in securing border areas near Arsal, the Lebanese government may push for a refugee transfer to safe zones on the other side of the frontier.

Boosting Hezbollah in Syria

The Arsal offensive is of great importance to Hezbollah, both in the short and long-term.

Having secured most of the Syrian side of the border, including through besieging Madaya and Zabadani nearby, to secure the other side would be a major tactical victory for its supply lines.

If Hezbollah increases its influence on both sides of the Syrian-Lebanese border, then, coupled with their expanded regional presence, they will be able to guarantee the smooth flow of weapons and supplies from Iran through Syria. In addition to Arsal, other areas near the eastern border, such as Baalbeck, have also been identified as key points in their regional supply routes.

Additionally, by playing a key role in combating Jabhat Fatah al-Sham, ISIS and similar groups, Hezbollah would be able to use these attacks to justify its resistance “enterprise.” In the past, it would refer to Israel’s violation of Lebanese territory and the occupation of Shebaa Farms as justification to remain armed. Going forward, Hezbollah can use its role in Syria and Lebanon against extremist groups such as ISIS as another justification.