A car bomb killed at least 32 people at a crowded transport hub in the Turkish capital of Ankara on Sunday and wounded at least 75 more, the second such attack in the administrative heart of the city in less than a month.
The blast, which could be heard several kilometers away, sent burning debris showering down over an area a few hundred meters from the Justice and Interior Ministries, a top courthouse, and the former office of the prime minister.
Police helicopters hovered overhead as a large cloud of smoke rose over the city center.
CCTV video posted online showed the blast and civilians fleeing the scene.
Photos and video posted to Twitter also showed the aftermath of the attack.
The Turkish government imposed a media blackout after the attack, and an Ankara court ordered a ban on access to Facebook, Twitter and other sites in Turkey on Sunday, after images from a car bombing in the Turkish capital were shared on social media, broadcasters CNN Turk and NTV reported.
Several local users reported difficulty in accessing the sites. Turkey last year blocked access to Twitter over the sharing of photographs of a prosecutor being held at gunpoint by far-left militants.
One senior security official told Reuters initial findings suggested the attack had been carried out by the Kurdistan Workers Party (PKK) or an affiliated militant group, but there was no immediate claim of responsibility.
The government blamed the PKK and Kurdish militants in Syria for the previous car bombing just a few blocks away on February 17, which killed 29 people, most of them soldiers. That attack struck near Turkey's military headquarters, parliament, and other key government institutions.
Today's attack was different, though, in that it appeared to target strictly civilian targets.
Islamic State militants have also mounted attacks in Turkey.
President Tayyip Erdogan spoke with Interior Minister Efkan Ala by telephone after Sunday's blast, presidential sources said.
"A total of 27 of our citizens were killed when a car exploded at Kizilay's Guven Park, and close to 75 of our wounded citizens were taken to various hospitals for treatment," the Ankara governor's office said in a statement.
A second senior security official said gunfire was heard after the blast.
State broadcaster TRT said the car had exploded at a major transport hub, hitting a bus carrying some 20 people near the central Guven Park and Kizilay Square. It said the area was crowded when the explosion happened at 6:43 pm local time.
NATO member Turkey faces multiple security threats. As part of a US-led coalition, it is fighting Islamic State in neighboring Syria and Iraq. It is also battling PKK militants in its southeast, where a 2.5 year ceasefire collapsed last July, triggering the worst violence since the 1990s.
The US embassy issued a warning on March 11 that there was information regarding a potential attack on government buildings in the Bahcelievler area of Ankara, several kilometers away from the site of Sunday's blast.
Islamic State militants have carried out at least four bomb attacks on Turkey since June 2015, including a suicide bombing which killed 10 German tourists in the historic heart of Istanbul in January. Local jihadist groups and leftist radicals have also staged attacks in the NATO member country in the past.