The battle for Qusair ended when the Syrian city fell to Hezbollah and Syrian regime forces on June 5 after a three-week assault against militant rebel fighters. It is no longer a secret that Hezbollah units were the main fighting force in the conflict, with the Syrian army’s role limited mostly to providing weapons support. During the fighting, Hezbollah carried out dozens of land assault operations. According to accounts attributed to Hezbollah fighters returning from the field, during the first days of the assault, the organization's units faced problems that its military leadership had not foreseen and that led to a number of losses among attacking units. Based on these accounts, the problems can be surmised as follows.
Hezbollah was surprised that many of its supposedly secret military tactics were known by the militants in Qusair, allowing them to prepare effective countermeasures. It is now widely believed within the party’s ranks that it was Hamas that divulged these secrets to the Qusair militants. Hezbollah and Hamas had had close military and security ties going back two decades. According to information leaked by sources inside Hezbollah, most of the sniping and booby-trap tactics that the party had shared with Hamas during joint training exercises in Lebanon and Syria were also used by the militants in Qusair. This, it is said, proves that Hamas partnered with Syrian opposition forces in the battle, at least in terms of providing technical assistance. Other information, as of yet unconfirmed, supposedly points to Hamas directly taking part in the Qusair battle with fighting units of its own.