Members of emergency services work at the scene of an explosion in Ankara, Turkey, Sunday, March 13, 2016. AP Photo 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.

The blast on Sunday, at a crowded transport hub in the city, killed at least 34 people and wounded 125 more.

Video footage showed burning debris showering down on what appeared to be the entrance to an underpass. The blast could be heard 2.5 km (1.5 miles) away and a large cloud of smoke could be seen rising over the city centre, a Reuters witness said.

A senior security official told Reuters that the blast appeared to have been caused by a suicide car bomb. A second security official said gunfire was heard after the blast. There was no immediate claim of responsibility.

The area, close to a courthouse and the Justice and Interior Ministries, was crowded when the explosion happened at 6:43 p.m., state broadcaster TRT said.

TRT said a vehicle had exploded at a major transport hub, hitting a bus carrying some 20 people near the central Guven Park and Kizilay Square.

The government has said the previous car bombing in Ankara on Feb. 17 was carried out by Kurdish militants. That attack struck near Turkey's military headquarters, parliament and other key government institutions.

Islamic State militants have meanwhile carried out at least four bomb attacks on Turkey since June 2015. Local jihadist groups and leftist radicals have also staged attacks in the NATO member country in the past.

(Reporting by Ece Toksabay and Asli Kandemir; Writing by David Dolan; Editing by Nick Tattersall)