A spokesman for the New Delhi police said Sunday that 10 to 12 people had been detained about the bombings. The police are studying video from closed-circuit television cameras at the market areas. Investigators have “vital” and “positive” clues, the police spokesman, Rajan Bhagat, said at a news conference.

Image Dazed victims struggled to recover Saturday after an explosion on Barakhamba Road in New Delhi, one of five crowded areas struck in coordinated bombings. Credit... Mustafa Quraishi/Associated Press

Prime Minister Manmohan Singh visited victims in a New Delhi hospital on Sunday, and high-level ministers held a series of meetings about improving security. “We have discussed various measures that may be needed not only in Delhi but other major cities” as well, the home secretary, Madhukar Gupta, told reporters on Sunday.

The attacks on Saturday evening were the latest in a series of bombings that have hit crowded areas in Indian cities in recent months. The makeshift bombs rely on easily obtained materials like ammonium nitrate for explosives and loose metal bits like screws and nails to inflict damage.

Image A bomb squad moved what appeared to be an unexploded bomb into a round safety chamber. Credit... Manpreet Romana/Agence France-Presse — Getty Images

Leaders around the world condemned the blasts. Pakistan’s newly elected president, Asif Ali Zardari, and its prime minister, Yousaf Raza Gilani, said in a statement that “the people and the government of Pakistan share the pain of the victims and bereaved families.” David C. Mulford, the American ambassador to India, said the United States “stands shoulder to shoulder with India in the fight against terror.”