Delhi explosions - cause?

There has been an explosion outside the high court in New Delhi, dozens of people are said to be injured. According to New Delhi-based news channel, NDTV, the blast took place just before the court opened for hearings. Meanwhile Reuters cite local TV networks and say that least 24 people had been injured. The New Delhi police have declined to comment on whether the blast was a bomb attack an if so who might be behind it. If it was a bomb I think we all know the background of the likely culprits.