"We reject negotiations with the usurping Israeli entity... We call for a historic and heroic stance by cancelling this negotiating meeting," Qassem said in a televised address.
He described the diplomatic efforts as a "ploy" designed to pressure Hezbollah into disarming and called the talks "pointless" given the ongoing Israeli military escalation.
The Lebanese and Israeli ambassadors to the United States are scheduled to meet in Washington on Tuesday to discuss holding direct negotiations between the two countries for the first time in decades.
Lebanese authorities have stressed that Beirut first wants to secure a ceasefire in the war. However, Israel has dismissed that prospect, saying it prefers instead to focus on "disarming Hezbollah and formal peace talks with Lebanon itself.
On 2 March, the Lebanese government outlawed all military and security activities by Hezbollah, accusing the group of "acting irresponsibly by launching rockets at Israel and drawing Lebanon into a regional conflict on behalf of Iran.
After an emergency cabinet meeting, Salam said: "The Lebanese state declares its absolute and unequivocal rejection of any military or security actions launched from Lebanese territory outside the framework of its legitimate institutions."
"This necessitates the immediate prohibition of all of Hezbollah's security and military activities, considering them to be outside the law, and obliging it to hand over its weapons".
PM Salam ordered the military and security agencies to take "immediate measures" to implement the cabinet decision and prevent "any military operation or the launching of missiles or drones from Lebanese territory."
Hours earlier, in response to the US-Israeli assassination of Iranian Supreme Leader Ali Khamenei at the start of their war on Iran, and as Israel amassed a hundred thousand soldiers at the Lebanese border, Hezbollah fired three rockets at Israel, which were intercepted and caused no injuries.
In six weeks of bombing, Israeli airstrikes have killed more than 2,000 and wounded nearly 7,000 people in Lebanon, destroyed 40,000 residential units, and displaced more than 1.2 million civilians.
In his speech on Monday, Qassem argued that Hezbollah was fighting a battle for the Lebanese against the Israeli occupation and aggression of the country, not someone else's wars, as critics say.
He argued that the Israelis, backed by Washington, have violated every single deal reached with Lebanon over the years.
Qassem also noted that the Israelis have violated the ceasefire in the course of 15 months between November 2024 and March 2026 on hundreds of occasions, with airstrikes killing and wounding hundreds of Lebanese civilians.
Hezbollah had said it implemented the terms of the truce by pulling its forces to the north of the Litani and ceased firing rockets at Israel, but the Israelis did not honour the deal.
Despite a ceasefire between the US and Iran that was reached on 8 April, Israel continued striking Lebanon despite confirmation from Pakistani mediators who negotiated a ceasefire between Washington and Tehran that Lebanon was part of the deal.
Hours after the start of the ceasefire went into force, Israel carried out a full-fledged massacre by bombing residential buildings in Beirut that killed 350 and wounded nearly 1,200.
In his speech, Qassem argued that "decisions of this magnitude cannot be made by the government alone and require a broad national consensus to be legitimate."
He asserted that "as long as the occupation exists, resistance and its weapons are a legitimate right," dismissing the government's recent attempts to declare Hezbollah’s military activities illegal.
Qassem urged the Lebanese government to insist that the Israeli side implement the terms of the November 2024 ceasefire, which mandated the end of hostilities and withdrawal of all occupation forces from southern Lebanon, as a precondition of any talks.
He decried what he described as the inability of the central government to stop ongoing Israeli aggression against the country.
Qassem accused the government of "backstabbing" the group by seeking to disarm it and aligning with "Israeli-American aggression" instead of condemning it.
He cautioned that bypassing national unity and making "free concessions" would only encourage further Israeli aggression and could lead to internal collapse.
Qassem also welcomed support from what he described as the "Axis of Resistance," including Iran, Yemen, and Iraq, stating that "Iran remains a primary supporter and that Hezbollah will always stand with it."
He framed the current war as an "existential defense" for all of Lebanon, not just one sect or group, against the threat of "Greater Israel".
He claimed that despite Hezbollah incurring heavy losses, Israel has failed to achieve its military objectives in Lebanon and that Hezbollah’s "steadfastness has frustrated the enemy's plans."
"We will not surrender," Qassem said as his fighters faced off with advancing Israeli troops in southern Lebanon. "We will remain in the field until our last breath."
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