Sheik Hassan Nasrallah said all preliminary investigations showed Takfiri groups, a term for Sunni radicals, were likely behind the bombing in a predominantly Shiite southern suburb of Beirut, as well as other recent attacks.
He also pledged to double the number of Hezbollah fighters in neighbouring Syria, who have travelled there to support the regime of President Bashar Assad.
"If you think that by killing our women and children ... and destroying our neighbourhoods, villages and cities we will retreat or back away from our position, you are wrong," he said in a speech to supporters marking the end of the 2006 monthlong war with Israel.
Yesterday's car bomb struck a crowded street in the Rweiss district in Beirut's southern suburbs, an overwhelmingly Shiite area and stronghold of Hezbollah. The explosion sent a massive plume of black smoke billowing into the sky, set several cars and buildings ablaze and trapped dozens of residents in their homes for hours.
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The group's fighters played a key role in a recent regime victory in the town of Qusair near the Lebanese border, and Syrian activists say Hezbollah guerrillas are now aiding a regime offensive in the besieged city of Homs.
Syrian rebels have threatened to retaliate against Hezbollah for intervening on behalf of Assad. Yesterday's car bombing raises the worrying specter of Lebanon being pulled further into the Syrian civil war, which is being fought on increasingly sectarian lines pitting Sunnis against Shiites.