File photo of twin bombing in Hyderabad, India. PHOTO: REUTERS.
Singh also visited the blast site in Dilsukh Nagar, where two bicycle bombs exploded within a few minutes of each other outside a cinema and near a bus stand on Thursday evening.
The prime minister met with some of the blast survivors and medical staff in two city hospitals and expressed his condolences.
"It is most important that in this hour of grief the people should maintain calm," he said.
"I am happy that the people of Hyderabad have refused to be provoked by this nefarious incident," the prime minister told reporters.
"I pray for the speedy recovery of those who have been injured, to those who have died I send my condolences to all the bereaved families," Singh added.
His spokesman Pankaj Pachauri told AFP Singh was scheduled to be briefed by N Kiran Kumar Reddy, chief minister of the southern state of Andhra Pradesh, on the incident.
Hyderabad, one of the major hubs of India's booming software industry, is the capital of coastal Andhra Pradesh.
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.
His Congress Party-led 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.
India's main opposition BJP party mocked the premier's one-day trip to Hyderabad saying the blasts were a result of the Indian government's failure to tackle terrorism.
"The prime minister's visit to Hyderabad is a non-event," BJP leader Balbir Punj told reporters in New Delhi.
"In fact, if he and his government had been sensitive to the issue of terrorism in this country... this attack would not have taken place," he said.
Andhra Pradesh Home Minister P Sabita Indra Reddy has said investigators have found "vital clues" but gave 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.
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I appears that Mr. Manmohan Singh has a single recorded video for media purposes, in case if there is any Bomb blast or Terrorist attack in India. Thanks Mr. Prime Minister (just to save time & resources of Nation, not its people)
Gulam Rasool "Kuldeep sharma" New Delhi