The head of Lebanon's powerful Shia movement also accused Saudi Arabia's ruling Al-Saud family of seeking to spark "a conflict between Sunni and Shia" Muslims.
"The execution (Saturday) of Sheikh Nimr al-Nimr reveals to the world the real criminal, takfiri and terrorist face of Saudi Arabia," Nasrallah said in a speech broadcast on Hezbollah's Al-Manar television.
Saudi Arabia to face 'divine revenge' over cleric's execution: Khamenei
"This is not something we can ignore," Nasrallah said.
Nimr, 56, was a force behind anti-government protests in Saudi Arabia in 2011 in the east of the country.
Shia anger after Saudi Arabia executes top cleric
He was executed along with 46 other men -- Shia activists and Sunnis who the Saudi interior ministry said were involved in Al-Qaeda killings. Some were beheaded and others were shot by firing squad.
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