A car bomb killed 27 people in the heart of the Turkish capital Ankara on Sunday and wounded 75 more, the governor's office said, less than a month after a similar attack killed 29 people just blocks away.

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. (1643 GMT), 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.