"The Secretary-General expresses his outrage over such deliberate attacks on people due to their religious beliefs in Pakistan," Ban's spokesperson said.
"He extends his heartfelt condolences to the families of the victims and to the Government and people of Pakistan," he added.
Ban strongly condemned the attack, terming it "appalling".
Armed men ambushed three buses near the city of Gilgit yesterday, forcing passengers off the vehicles and then shot down 25 Shia Muslims.