Sky News reports the explosion went off around 6:15 p.m. local time and appeared to be "aimed at the heart of the state." Sky correspondent Alex Rossi in Ankara points to the explosion's proximity to Turkey's parliament building as well as the military complex.
He adds that it's "very very concerning for the Turkish government that this happened really so close to sort of very important state institutions."
Peter says there was no immediate claim of responsibility for the attack.
"Kurdish rebels, the Islamic State group and a leftist extremist group have carried out attacks in the country recently," The Associated Press reports.
The wire service adds that the Turkish government "imposed a gag order which bans media organizations from broadcasting or printing graphic images of the dead or injured from the scene of the explosion."
The U.S. ambassador to Turkey, John Bass, tweeted condolences after the attack:
Amb. Bass: Deeply saddened, shocked by terror attack in Ankara. Our hearts and prayers go out to those affected.