Belaid was killed this week as he left for work in Tunis. As leader of the Tunisian Democratic Patriots Movement, the Italian government described Belaid as a symbol of the Jasmine Revolution.
"We are deeply disturbed by the death of Chokri Belaid," Terzi said in a statement. "Episodes of this kind cannot and must not in any way alter our faith in the democratic processes under way in Tunisia and in the other countries of the Arab Spring."
Similar statements were released by the U.S. and British governments.
Unrest followed the assassination and labor unions in Tunisia have called for a general strike. Ruling Islamist party Ennahda rejected a call from Prime Minister Hamdi Jebali to form a new government, reports al-Jazeera.
Eric Goldstein, deputy director of Middle East programs at Human Rights Watch, said the Tunisian history of non-violence was in jeopardy following Belaid's assassination.
A protest suicide in Tunis in December 2010 sparked a series of uprisings across the Middle East and North Africa.