Sheikh Naim Kassem told Lebanon's leading An-Nahar daily that Hizbullah's "resistance" to Israel would continue, saying "justifications for ending it do not exist."
Kassem said Hizbullah was surprised by the magnitude of Israel's response to the group's capture of IDF soldiers Eldad Regev and Ehud Goldwasser.
Hizbullah had expected Israel to respond at most with "some limited attacks" and two or three days of bombing, Kassem said.
"We were surprised by the size and strength of the Israeli reaction. We expected that the IDF would bomb areas close to the border for several days and only cause minimal damage," he said. "In the last days [of the war], the enemy exercised military hysteria... The size of the aggression was beyond our expectation."
In addition to pounding Hizbullah's strongholds in east and south Lebanon and Beirut's southern suburbs, Israeli warplanes and artillery also targeted Lebanese infrastructure, destroying bridges and roads throughout the country and bombing Beirut's airport and ports.
According to Kassem, Hizbullah had information that the US and Israel were planning an attack against the organization in September or October, but due to American and Israeli public pressure following the kidnapping of the two soldiers, the attacks were carried out earlier.
Kassem, whose son was badly wounded in the 34-day fighting, said Hizbullah would coordinate with the Lebanese army as it deploys in parts of south Lebanon controlled by the guerrillas. But he said the group would keep its weapons despite the deployment of more UN peacekeepers as well.
"When we agree on a defensive plan to confront Israel, defining the job of the resistance, the army and the Lebanese people, then we will see what the rules and roles are," Kassem said.
Hizbullah has said that it would not surrender its weapons as long as Israel holds Lebanese prisoners, occupies the Shaba Farms and IAF planes fly in Lebanese airspace.