The head of Lebanon's powerful Shiite movement also accused Saudi Arabia's ruling Al-Saud family of seeking to spark "a conflict between Sunni and Shiite" Muslims.
"The execution (yesterday) 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.
"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.