"The United States strongly condemns today's terrorist attack on civilians in Pakistan, and we offer our condolences to the families of the victims and all the people of Pakistan," Clinton said.
Her comments came after a suicide bomber drove a truck filled with explosives onto a sports field during a volleyball came in Laki Marwat, a city in northwest Pakistan.
"The Pakistani people have seen terrorists target schools, markets, mosques, and now a volleyball game," the secretary said.
"The United States will continue to stand with the people of Pakistan in their efforts to chart their own future free from fear and intimidation, and will support their efforts to combat violent extremism and bolster democracy."
The attack occurred near the Waziristan tribal region, believed to be home to Taliban and al-Qaida training bases, where government forces have been battling Taliban militants.