National capital Delhi, Mumbai and other major cities in the country have been put on high alert and security beefed up at all important buildings and markets after serial blasts rocked the city of Hyderabad, officials said.
"The city is on high alert and security has been stepped up. The number of armed security personnel at all important buildings and markets has been increased," a senior Delhi police officer said.
Andhra Pradesh Police began search operations with dog squads in several busy market areas in the city and its twin city Secunderabad to foil any explosives.
Security was beefed up at Rajiv Gandhi International Airport at Shamshabad, state secretariat, Charminar and other vital installations, a police official said.
An alert was also sounded in coastal city of Visakhapatnam, temple town of Tirupati and other major towns across the state.
Police on Thursday sounded a high alert in parts of Karnataka, including Bangalore. Alert has been declared in parts of Punjab, Uttar Pradesh, Maharashtra, West Bengal and other states. Security has also been tightened at the Jammu and Kashmir border.
At least 13 people were killed and 80 injured in the twin blasts near two theatres in Dilsukhnagar, a busy commercial area in the southern part of Hyderabad, about 15km from the heart of the city.