The Union Home Ministry has sounded a nationwide alert with special stress on four major cities - Delhi, Mumbai, Bangalore and Hyderabad - in wake of the blast in Varanasi. "A general alert has been sent to all state governments and they have been asked to stay on high alert,” Union Home Secretary G K Pillai said in New Delhi. “It was low intensity blast which occurred at about 6.20 PM in which three-four people were injured. Subsequently we understand there could have been a stampede. As a result 15-20 people were injured. So roughly 20-25 people injured,” he said.