The attack has the trademarks of Kashmiri Islamic terrorist groups like the Lashkar-e-Toiba which has set off bombs in quick succession in Indian cities before. India's domestic intelligence agency, the Intelligence Bureau, claims that this attack, as also the grenade attacks in Jammu and Kashmir earlier today were aimed at diverting attention from the elections being held in Pakistani Kashmir.

It does sound like Pakistani/Kashmiri separatists are adopting the style of 'Al Q.'

Several blasts rock Mumbai commuter trains - Wikinews