Three men stabbed worshippers at the Imam Hussein (AS) mosque in Verulam near Durban‚ killing one and critically injuring two others.
The attackers, who stormed the building shortly after noon prayers on Thursday, also set the mosque on fire.
Qassemi on Friday condemned the attack and sympathized with the South African government, people and families of the victims.
He underlined the need for prompt investigation into the incident identifying the perpetrators and bringing them to justice.
Qassemi further described the attack as a move aimed at creating insecurity and fomenting discord, stressing the need for a serious campaign against extremism and Takfiri terrorism by all countries.