President Obama called the principal of the Pittsburgh-area high school where a teenager stabbed two dozen people earlier this week to express his sympathy, the White House said Thursday.

Press secretary Jay Carney said Obama called Principal Ron Suvak of Franklin Regional High School while flying back to Washington aboard Air Force One.

According to Carney, Obama expressed his concerns and sympathy over the stabbings.

The attack occurred Wednesday morning, shortly before Obama left for Texas. While there, he spoke at the memorial service for the victims at Fort Hood, where a gunman killed three and injured more than a dozen others before taking his own life last week. He also spoke at an event marking the 50th anniversary of the signing of the Civil Rights Act.

None of those stabbed were killed, although some remain in critical condition.