Sheikh Hassan Nasrallah was speaking at a rally in the southern Beirut suburb of Roeis on Wednesday, two days after Hizb Allah and its ally Shia Amal took all 23 seats in the parliamentary elections in South Lebanon.
The US, which considers Hizb Allah a terrorist organisation, expressed concern over the party's success, saying an armed militia should not have a role in a democratic system.
"Don't waste your time thinking about what the Americans say," Nasrallah told the crowd of thousands. Referring to the legislature's 128 seats, he added: "Even if the Lebanese people, all the people of Lebanon, elected 128 Hizb Allah members as legislators, the American administration would still say that Lebanon, its parliament and its people, are terrorists that should be wiped out."
"Death to America!" the crowd shouted in response.
For his part, Hizb Allah's deputy secretary-general, Naim al-Qassem, has left open the possibility of the movement entering the government for the first time.
Aljazeera on Wednesday quoted al-Qassem as saying: "The victory of Hizb Allah in the legislative elections in South Lebanon amounted to a stunning blow to plots hatched by outside parties for interference in Lebanon. It would put an end to efforts aimed at disarming the resistance (Hizb Allah)."
The Hizb Allah sees its victory as
a rebuff to US-French pressure
He described Hizb Allah's electoral sweep in South Lebanon as a "referendum on the popularity of the resistance and rejection of foreign interference in Lebanon's internal affairs".
Wednesday's Hizb Allah rally in Beirut was held to back the Mount Lebanon Unity ticket, which includes a Hizb Allah member as well members of Druze leader Walid Jumblatt's Progressive Socialist Party and the Lebanese Forces, the main Christian militia during Lebanon's 1975-90 civil war.
Nasrallah urged Hizb Allah supporters to back Mount Lebanon Unity, saying it believed in "protecting the resistance" - the term for Hizb Allah's military wing.
"On Sunday, we will support this list and vote for all its members," he said.
The US has been calling for the implementation of UN Security Council Resolution 1559, which calls on Hizb Allah to lay down its arms.
"Even if the Lebanese people, all the people of Lebanon, elected 128 Hizb Allah members as legislators, the American administration would still say that Lebanon, its parliament and its people, are terrorists"
The group has refused to do this, and has received support from the Lebanese government, which argues that Hizb Allah is not a militia but a resistance movement against Israel.
Druze leader Jumblatt and his electoral ally, Saad al-Hariri, the son of the slain former prime minister Rafik al-Hariri, have been visited by Western politicians, including US senators, for their role in pushing for the withdrawal of all Syrian forces from Lebanon.
The foreign politicians are known to support the opposition's aim of wresting control of the legislature from pro-Syrian legislators.
The Syrian military withdrawal, which was completed in April, was opposed by Hizb Allah, which received support from Syria and Iran.
But, in the shifting allegiances of Lebanese politics, Jumblatt and al-Hariri have now made tactical alliances with Hizb Allah.
The staggered elections began on 29 May and end later this month.