A car bomb exploded in Ankara killing 34 people and wounding more than 100, the second deadly attack in the Turkish capital in a month.
The massive blast rocked an area that houses the Justice and Interior ministry buildings and a top courthouse. It was heard several kilometers away.
The suicide attackers had driven up to the Guven Park in the administrative heart of the city in Kizilay district in a BMW car, officials said.
The explosives-laden car hit a bus carrying some 20 people at a major transport hub, reducing the area into a pile of wreckage.
Security officials believe the attack was plotted by the though there was no claim yet, Reuters reported.
Turkish security officials said they will name the perpetrators of the car bombing on Monday after they complete initial investigations.
"These attacks, which threaten our country's integrity and our nation's unity and solidarity, do not weaken our resolve in fighting terrorism but bolster our determination," Turkish President Tayyip Erdogan said in a statement.
In February, an attack on a military bus in the city centre had killed 28 people. The bomb attack was claimed by the Kurdistan Freedom Hawks (TAK), a Kurdish militant group affiliated to the PKK.
In October a suicide attack on a peace rally had killed more than 100 people in Ankara.
The United States had warned of a terror strike on the Turkish capital two days ago. "This horrific act is only the most recent of many terrorist attacks perpetrated against the Turkish people. The United States stands together with Turkey, a NATO ally and valued partner, as we confront the scourge of terrorism," a White House statement said.
Local newspapers reported that a court has banned people from using social media platforms like Facebook and Twitter in order to prevent the sharing of images of the attack.
Security officials said the explosives used in the attack were similar to those used in the February 17 attack on the military convoy.