"The ongoing Israeli threat forces the resistance to continue to boost its capacity ... in order to fulfil its role in liberating occupied territory," he said on Monday in a rare news conference to present Hezbollah's new political manifesto.
"The Israeli threat ... calls for Lebanon to have a defence strategy built on the presence of a popular resistance that helps to defend the country against Israeli aggression and a national army that protects the country and its stability."
Nasrallah accused the US of being the world's leading exporter of terrorism and urged nations around the globe to stand up against such a threat.
"There is no question that American terrorism is the origin of all terrorism around the world," he said.
The US officially considers Hezbollah a terrorist organisation.
Nasrallah accused George Bush, the former US president, of having turned the US into a threat for the rest of the world.
"If a survey were to be held today, the United States would be the most hated nation in the world.
"Standing up to the US threat must be a worldwide effort," he added.
"This is a delicate and difficult task ... and one that will involve generations to come."
Hezbollah fought a fierce war with Israel in 2006 that destroyed much of southern Lebanon.
The party is the only faction which refused to disarm after Lebanon's 1975-1990 civil war.
It argues that its weapons are needed to protect the country against Israel, which withdrew its troops from south Lebanon in 2000 after a 22-year occupation.
In presenting Hezbollah's 32-page political manifesto, Nasrallah ruled out any chance of ever recognising Israel and insisted on the right of the Palestinians to reclaim their homeland.
"We categorically reject any compromise with Israel or recognising its legitimacy," he said.
"This position is definitive, even if everyone recognises Israel."
He insisted that Hezbollah, which has been accused of acting as a state within a state, was keen on a united Lebanon that represents everyone.
"We want a Lebanon that is united through its land, its people, its state and institutions," Nasrallah said, rejecting any notion of the country being divided along confessional lines.
Hezbollah's first manifesto in 1985 called for the establishment of Islamic rule in Lebanon, but the party leadership has toned down its rhetoric in recent years as it gained political clout.
Nasrallah, 49, has headed Hezbollah since 1992 when his predecessor, Abbas Moussaoui, was killed in an Israeli helicopter raid. The party has participated in the Lebanese government since 2005.