U.S. officials said they remained determined to fight terrorism in the wake of Tuesday's Taliban attack that left 141 Pakistanis dead, most of them schoolchildren.
President Barack Obama decried the "heinous" attack in Peshawar and said the U.S. would continue to support Pakistan's efforts to combat terrorism and extremism.
White House spokesman Josh Earnest said the "depraved decision that one has to make to storm a school of innocent children and fire on them is a testament to how cold-blooded these extremists are."
Speaking from London, Secretary of State John Kerry called the killings an act of terror that "shakes all people of conscience."
"The images are absolutely gut-wrenching: Young children carried away in ambulances. A teacher burned alive in front of the students. A house of learning turned into a house of unspeakable horror," Kerry said.
"Prime Minister [Nawaz] Sharif said, 'These are my children, it is my loss.' Well, this morning, wherever you live, wherever you are, those are our children. And this is the world's loss," the secretary added.
At the State Department in Washington, spokeswoman Jen Psaki said the U.S. stood beside the Pakistani people in their fight against extremism and would continue assisting them on counterterrorism measures.
"We're going to keep working together, and I don't think it reflects anything other than a cowardly attack by this group," Psaki said.
At the Pentagon, spokesman Rear Admiral John Kirby called the Tuesday massacre a grim reminder of the "real" terrorist threat that remains around the globe.
"When you see something like what happens today and the recent attacks we've seen in Kabul, I think it just steels all of us – not just Afghans, not just Pakistanis, not just Americans, but all of us, all of the coalition and partner members – to make sure that we continue to stay dedicated at this going into 2015," Kirby said.
He said that while the Afghan Taliban and the Pakistani Taliban are not viewed as one homogenous group, the violence they cause is a common consequence that must be stopped.
Some information for this report came from Reuters.