Nasrallah was quoted by Lebanese newspaper Al-Safir as telling a meeting of party backers that the terrorist group of Islamic State in Iraq and the Levant (ISIL) could have spread to Lebanon if Hezbollah had not stepped in.
"If we had not intervened in Syria at the appropriate time and in the appropriate way ... ISIL would now be in Beirut."
Nasrallah praised calls by Shi'ite clerics in Iraq for volunteers to take up arms against ISIL, whose swift advance through majority Sunni areas of northern Iraq threatens civil war and a possible break-up of the country.
"The aim of this (call) was not to protect a specific sect, but to protect all of Iraq," Nasrallah said.
The Hezbollah chief also wondered why the party's critics have not condemned ISIL's advance on the Iraqi capital.
Nasrallah also hinted that some regional and Persian Gulf Arab regimes were involved in the fighting in Iraq.
“Who is benefiting from what's going on there?” he asked.
He also raised doubt about Washington's stance as it weighs possible drone strikes against the ISIL terrorists.
Nasrallah expressed relief over the improvement of the security situation in Lebanon. But warned that “this does not mean things have gone back to normal.”
“We should always take precautions,” he said.
He reiterated the need to elect a president who “does not stab the resistance in the back.”
Lebanon has been without a head of state since the expiry of Michel Suleiman's six-year term on May 25.
Parliament failed to elect a successor over differences between the March 8 and 14 alliances on a compromise candidate.
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