"The rumors spread in the previous days made me hold an urgent media appearance to show you that I am in good health. ... There is a media campaign against Hezbollah," Nasrallah said Wednesday night in a short speech riddled with coughs.
It wasn't clear when and where the speech was recorded but Hezbollah's al-Manar satellite station aired the speech in full.
Nasrallah was referring to media reports in recent days claiming he had been flown to Tehran to undergo medical treatment for cancer.
He said he decided to appear on television to say "these rumors are baseless," the Lebanese Ya Libnan website quoted him saying.
He also denied reports claiming his deputy Naim Qassem was seriously injured in an explosion that occurred near a convoy in Syria earlier in the day calling them "lies." Qassem was said to have assumed command of the organization while Nasrallah was away.
The Lebanese website quoted a Beirut radio report earlier in the week that said Nasrallah, 52, was taken to Tehran on an Iranian presidential plane. The Voice of Lebanon radio station said Nasrallah went to Tehran for emergency medical treatment for severe cancer-related complications.
On Tuesday the Turkish Anadolu news agency reported Nasrallah's health had deteriorated and he was transferred from a private hospital in Beirut to Tehran.
Since the Second Lebanon War in 2006, Nasrallah has rarely appeared in public and delivers televised speeches from undisclosed locations.
Syrian fighter plane shot down, Israel claims
U.S., allies launch airstrikes against Syria