At the gathering in Beirut, Nasrallah told followers that Hezbollah's fighters will remain in Syria to "defend Lebanon, Palestine, the Palestinian question and Syria, the protector of the resistance."
His comments likely will anger rival Lebanese politicians who have said that Hezbollah's withdrawal from Syria is a precondition for the organization joining a new government. Lebanon's prime minister-designate, Tammam Salam, has not been able to form a Cabinet since April as a result of political disagreement between rival groups mostly over Syria's civil war, which has sharply divided the Lebanese.
"It is shameful to turn the commemoration of Ashoura into an occasion to declare standing beside an oppressive regime against an oppressed people," said former Prime Minister Saad Hariri in a statement released by his office in Beirut. "We will not offer Hezbollah any form of national legitimacy for its reckless policies that throw Lebanon in the regional storms."
Meanwhile, Lebanese security officials said at least seven rockets fired from Syria on Thursday fell in the eastern village of Nabi Sheet, a Hezbollah stronghold, but caused no casualties. Such attacks have been common since Hezbollah joined Assad's forces.
Also Thursday, Syrian army helicopters fired several rockets on an area along Lebanon's border near the eastern town of Arsal, said the Lebanese officials, who spoke on condition of anonymity in line with regulations. It was not clear if the fire caused any casualties or if the missiles struck inside Lebanon.
The massive Hezbollah ceremony in Beirut was held amid tight security, including a ban on vehicles in the area, following huge bombings last summer that killed and wounded dozens of people.
Ashoura commemorates the 7th-century death of Imam Hussein, the Prophet Muhammad's grandson, and is a major annual event for Shiite Muslims, marked by somber marches and processions.
Nasrallah, who lives in hiding, has made few public appearances since his group fought a 34-day war with Israel in 2006 for fear of assassination by Israel. Thursday was his third public appearance this year.