Shaikh Hasan Nasr Allah's comments on Sunday came amid tension between his group and anti-Syrian politicians, some of whom are calling for disarming Hizb Allah.
"Whoever dreams about getting rid of Hizb Allah in any position is mistaken," Nasr Allah said in a speech at a graduation ceremony for 1300 Hizb Allah members and supporters.
Nasr Allah criticised US ambassador to Lebanon Jeffrey Feltman and Assistant US Secretary of State David Welch, who have been accused by Hizb Allah of interfering in Lebanese affairs.
Welch told Lebanon's LBC Television on Thursday that Hizb Allah should not be in the government and that the United States does not consider it a militia but a terrorist organisation.
"Whoever wants to work to get rid of Hizb Allah will repent it and will be mistaken," Nasr Allah said.
The Lebanese government says Hizb Allah is a resistance movement.
UN Security Council Resolution 1559, issued in 2004, calls for the disarmament of all militias in Lebanon - a reference to Hizb Allah and Palestinian resistance factions.
"Whoever wants to work to get rid of Hizb Allah will repent it and will be mistaken"
Shaikh Hasan Nasr Allah,
Hizb Allah leader
Hizb Allah says its weapons are a deterrence against future attacks by Israel, which twice invaded Lebanon in 1978 and 1982. Since the Israeli withdrawal in 2000, Hizb Allah has continued to fight Israel over a disputed patch of land on the border where Syria, Lebanon and Israel meet.
Some anti-Syrian politicians have said Hizb Allah should disarm now since Israel has withdrawn from Lebanese territory.
"At the moment we feel that someone is carrying out this (American) dictation, we will not be shy and we will speak openly," Nasr Allah said. "Whoever colludes in such an American conspiracy is a Zionist, an Israeli and a Sharonist," he said in reference to Israel's ailing Prime Minister Ariel Sharon.