Qassem was speaking for the first time since the start of the ceasefire on Wednesday that envisions both Hezbollah and the Israeli military withdrawing from south Lebanon and the Lebanese military deploying there alongside UN peacekeepers.
"We will work to... strengthen Lebanon's defensive capacities," said Qassem, who succeeded Hezbollah's former leader Hassan Nasrallah after he was killed in a massive Israeli air strike on south Beirut in September.
"The resistance will be ready to prevent the enemy from taking advantage of Lebanon's weakness along with our partners... first and foremost the army," he added in a televised speech.
"The coordination between the resistance and the Lebanese army will be at a high level to implement the commitments of the agreement," Qassem continued, adding that "no one is betting on problems or disagreements" with the army.
Qassem also declared that his group had achieved a "great victory" against Israel that "surpasses that of July 2006", referring to the last time Hezbollah went to war with Israel.
"We won because we prevented the enemy from destroying Hezbollah... (and) from annihilating or weakening the resistance."
Qassem vowed that "our support for Palestine will not stop and will continue through different means".
'Threat thwarted'
The truce ended a conflict that began the day after Hamas's unprecedented October 7, 2023 attack on Israel, when Hezbollah began a low-intensity exchange of cross-border fire in solidarity with their Palestinian allies.
In late September, Israel intensified its campaign against Hezbollah, launching fierce air strikes and later sending in ground troops.
Lebanon's health ministry said at least 3,961 people have been killed in the country since October 2023 as a result of the conflict, most of them in recent weeks, while 16,520 were wounded.
On the Israeli side, the hostilities with Hezbollah killed at least 82 soldiers and 47 civilians, authorities there say.
Earlier Friday, the Israeli military said it struck a Hezbollah rocket launcher in southern Lebanon after detecting militant activity in the area.
"A short while ago, terrorist activity and movement of a Hezbollah portable rocket launcher were identified in southern Lebanon," the army said.
"The threat was thwarted in an (Israeli Air Force) strike," it added in a statement that featured a video of the air strike on a slowly moving truck.
Israel has vowed to continue acting against any threats even after the ceasefire.
The military also announced a nighttime curfew in south Lebanon for the third day in a row, warning residents they are "strictly forbidden to move or travel south of the Litani River" between 5:00 pm (1500 GMT) on Friday and 07:00 AM (0500 GMT) the following day.
Under the ceasefire agreement, Israeli troops will hold their positions but "a 60-day period will commence in which the Lebanese military and security forces will begin their deployment towards the south", a US official told reporters on condition of anonymity.
Then, Israel should begin a phased withdrawal without a vacuum forming that Hezbollah or others could rush into, the official said.
