"The fact that this attack occurred ahead of a planned rally for peace underscores the depravity of those behind it and serves as another reminder of the need to confront shared security challenges in the region," National Security Council spokesman Ned Price said in a statement.
Two suicide bombers likely carried out the twin explosions near Ankara's main train station, Turkish Prime Minister Ahmet Davutoglu said, where groups of leftist and pro-Kurdish activists had gathered for the anti-government peace rally.
"We offer our deepest condolences to the families and other loved ones of the victims, just as our thoughts remain with those injured in this senseless violence," added Price.
"The United States will continue to stand side-by-side with the Turkish government and people as together we take on the scourge of terrorism.
"Far from deterring these efforts, such horrific acts of violence will only strengthen our resolve.