The comments today from former Prime Minister Saad Hariri come two days after a deadly car bombing struck a Hezbollah neighbourhood south of Beirut. Many people see the blast as retaliation for Hezbollah's armed support for Syrian President Bashar Assad.
Nasrallah on Thursday blamed Sunni extremists for the blast and said he was prepared to double the number of Hezbollah fighters in Syria if the bombing is linked to that conflict.
Hariri said on his official Twitter account that Nasrallah's speech "drags Lebanon further into the Syrian fire, and it is a pity to squander the blood of Lebanese in such a way.