The scene of the explosion is located in close proximity to Turkey's parliament, the Presidency of the General Staff, and Army, Air Force, Navy and Coast Guard commands.
A Turkish military general staff official has confirmed to Reuters the explosion targeted a bus carrying military personnel.
"Social media users in Ankara say they heard a loud noise all across the city, and a huge plume of smoke rising over downtown Eskisehir Avenue."
CNN Türk said that military lodging facilities were targeted and there were a large number of casualties.
Twenty ambulances were sent to the scene of the blast, media reported, citing medical officials.
Last October several explosions at a peace rally in the Turkish capital killed more than 100 people and injured dozens more. The explosions appeared to be the result of suicide bomb attacks.
Prime Minister Ahmet Davutoglu canceled his trip to Brussels which was due later on Wednesday, an official in his office said.
Deputy Prime Minister Bekir Bozdag has condemned the attack, which he called “terrorist” on his Twitter account, RT reported.
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