Indian PM flies to Hyderabad after deadly blasts

"The prime minister is going to visit the injured in hospital and then he will be briefed by the (Andhra Pradesh state) chief minister," Singh's spokesman Pankaj Pachauri told AFP by telephone from the southern city.

Singh is also scheduled to visit the blast site in Dilsukh Nagar, where two bicycle bombs exploded within a few minutes of each other outside a cinema and a bus stand on Thursday evening, according to the Press Trust of India.

The premier has vowed to bring to justice the perpetrators of what he called a "dastardly" attack, the first major bombings in India since 2011.

The government was criticised in parliament on Friday by the opposition, which said the bombings had exposed systemic security failures at a time when India is on heightened alert.

Andhra Pradesh Home Minister P. Sabita Indra Reddy has said investigators have found "vital clues" but given no details.

Newspapers have pointed the finger at the Indian Mujahideen, a banned militant outfit which has claimed responsibility for previous attacks.

The fitting of the explosive devices to bicycles was similar to other attacks by the outfit, local media reports quoted investigators as saying.

The homegrown group has links to Lashkar-e-Taiba, the Pakistan-based militant outfit blamed for the 2008 Mumbai attacks that claimed 166 lives, according to Indian intelligence officials.

New Delhi has long accused its neighbour of aiding and abetting the militant groups who have carried out attacks on Indian soil -- a charge that Pakistan rejects.