In mid-November 2013, the Syrian military, backed by Hezbollah, launched an offensive against the rebel-held Qalamoun Mountains in an attempt to cut rebel supply lines to Damascus from Lebanon.

[35][36] By 3 April, the Syrian military had advanced on three axes towards Zabadani, securing the western and eastern approaches to the city, and relatively paralyzing the defending rebels.

[44] Early on 4 May,[45] the al-Nusra Front and allied Islamists launched a preemptive attack against SAA and Hezbollah forces, and by the next day captured several positions.

[54] The withdrawing militants also reportedly left behind 150 heavy machine guns (from 12.7 to 23 mm caliber) and anti-tank rockets (firing range from 3.5 to 5 kilometers).

[11] On 11 May, the Army and Hezbollah captured the Al-Barouh hill outside Al-Juba, taking total control of the outskirts of the village,[55] and seized the border-crossing at Ma'br Al-Kharbah.

[58] Despite the fighting taking place over the previous week, an all-out battle had reportedly not yet started,[11] with some predictions of it happening in the second half of the month.

[59] According to Mario Abou Zeid from Beirut's Carnegie Middle East Center, Syrian Intelligence directed its operatives within ISIL in Qalamoun to launch probing skirmishes against FSA forces to test their defenses, and in an attempt to distract them from the main battle.

[64] On 13 May, the Syrian Army and Hezbollah took full control of Tallat Mussa[21][65][66] after capturing at least nine rebel positions during heavy exchanges of artillery and rocket fire along the ridge between Al-Juba, Ras al-Maara and Assal al-Ward.

Earlier in the day, Army troops, backed up by Hezbollah, seized half of the outskirts of Ras al-Maara and advanced toward the highlands of Jabal al-Barouh which is linked to Tallat Mussa.

[69][70] The Syrian Army also claimed to have captured the hills of al-Jerafah, Sin al-Sakhrey, al-Reya, Ouqbet al-Faseh, and all of the barrens of Ras al-Maara.

[74] Hezbollah clashed with militants at Jabal al-Barouh,[73] while it took control of the Ras al-Marra-Arsal border-crossing, which was the last border entry into Qalamoun from Lebanon,[74] as well as Dahr al-Hawa Hill, which overlooks Arsal and Younin.

[5] During the day, after reaching a "point of desperation", al-Nusra attacked and recaptured the Ras al-Marra border-crossing, after which it assaulted Tallat Mussa but was repelled.

[85] On 21 May, the Army and Hezbollah advanced further, capturing additional peaks and fully besieging the al-Nusra Front in a small portion of the mountains, as they were in full control of all of the border crossings in the Qalamoun region by this point[22] and had regained 310 out of 780 square kilometers of Lebanese and Syrian territory seized by rebels.

[86] On 25 May, Hezbollah and the 20th and 128th Brigades of the 1st Armored Division captured the western hills of Tal Thaljah, after al-Nusra made an attempt to counterattack the advancing Syria government forces on the hilltop, but was repelled.

[87] The battle for Tal Thaljah was the bloodiest for Hezbollah with six of their fighters dead as they fought uphill with no air cover due to bad weather.

[88] With this advance, government forces were in nearly total control of the Qalamoun Mountains on the Syrian side of the Syria-Lebanon border,[87][89] and thus concluded their offensive.

[88][90] On 29 May, pro-government Al-Masdar News reported that the Syrian Army and Hezbollah had captured 90% of the Qalamoun Mountains, with the remaining 10% located on the Lebanese side of the Syria-Lebanon border[91] and under ISIL control.

[97] Syrian Army and Hezbollah advances in the western rocky barrens continued the next day,[98] as they captured the strategic hill that overlooks Jaroud Jarajeer at Qurnah Shab'ah.

[23] The next day, Nasrallah stated the Syrian Army and Hezbollah were in control of the major parts of the mountain range, after defeating the Al-Nusra Front, and had begun a battle against ISIL.

[105] On 23 June, the 20th and 128th Brigades of the Syrian Army's 1st Armored Division, in coordination with Hezbollah and the NDF, advanced to the Jaroud Qarah area and launched an assault on ISIL defensive positions, which was the last ISIL-controlled part of the Qalamoun mountains in Syria.

The Hezbollah also set itself out to recapture the Lebanese border-district of Arsal, from where the Jabhat Al-Nusra and ISIL have been receiving much of its reinforcement into the Qalamoun Mountains.

[112] Sami Nader, a professor in politics at the University of Saint Joseph in Lebanon stated regarding Iranian and Hezbollah involvement in the offensive; "they are in desperate need for an achievement to counter balance their losses; they need to sell it to their constituents in order to justify the continuing battle and involvement in Syria" adding that "Qalamoun is more of a media campaign than a real battle on the ground".

[115] The Washington Institute for Near East Policy agreed with this assessment by stating that "even his [Assad's] most reliable Shiite allies may not be able to sustain him as the war's attrition increasingly highlights his demographic disadvantage".