The explosion hit three military vehicles and a private vehicle in central Ankara, near Turkish Parliament buildings, Turkey's semiofficial Anadolu news agency reported, citing Ankara Gov. Mehmet Kiliclar, CNN said.
The vehicles were stopped at a traffic light at the time, the military said.
Authorities believe a bomb-laden vehicle caused the explosion, Kiliclar said, according to Anadolu.
The military consider the blast to be a terror attack. No group has claimed responsibility.
"Our determination to respond in kind against such attacks against our unity and future from outside and inside is even more strengthened through such attacks," Turkish President Recep Tayyip Erdogan said in a statement. "Turkey will not hesitate to use its right to self-defense anytime, anywhere, and in all situations."
Soner Cagaptay, a senior fellow at the Washington Institute for Near East Policy think tank, said that if it was a bomb attack, suspects could include ISIS or the PKK, the Kurdish militant separatists that Turkey considers a terrorist group.
"There are definitely many reasons why Turkish reaction is going to be fierce" if this was an attack, he said.