Tunisian opposition leader Chokri Belaid was killed this week as he traveled to his office in Tunis. He was the leader of the Democratic Patriots Movement, a party that helped lead the country's Jasmine Revolution.
Ban, in a statement issued through his spokesman, said democratic transition should continue to develop in Tunisia despite tensions following Belaid's death.
"Tunisia's democratic transition should not be derailed by acts of political violence," his statement read.
Belaid's funeral was Friday. Labor leaders called for a general strike in a country shaken by his slaying.
Tunisia's revolution ended the 24-year rule of former President Zine el-Abidine Ben Ali and ushered Islamic party Ennahda to power. The ruling party this week rejected calls for a new government.
Amnesty International last year took note of the promise of basic freedoms given post-revolutionary elections. The organization said, however, that the police and other state institutions continued to commit human rights abuses.
"There has been important progress in Tunisia's transition," Ban's statement read. "Yet, much remains to be done in terms of the constitutional process and with regard to meeting the social and economic demands of the Tunisian people."