Investigators examined forensic evidence, worked on sketches and searched for tell-tale clues at the site of twin explosions that ripped through the southern Indian city of Hyderabad Thursday killing 16 people and wounding 119.

The blasts occurred soon after sunset, within a span of about two minutes, in a movie theater parking lot and at a bus stop in Dilsukhnagar, an area on the city’s outskirts full of restaurants and tea shops.

The blast sites were about 400 feet apart, Hyderabad police said. Television images showed the area littered with shattered glass, blood-soaked clothes, bags and shoes, and people rushing around in panic.

There was no immediate assertion of responsibility for the attacks, and police did not identify any suspects.

A police officer told reporters in Hyderabad that improvised explosive devices may have been placed on two bicycles at the site. But he added that a surveillance camera in the area was not functioning, and police did not have video footage to assist their investigation

Home Minister Sushil Kumar Shinde said several Indian cities had been put on high security alert before the explosions, after warnings were received.

“We got some information two days ago about a possible attack, though it was not specific about what kind of an attack, or where,” Shinde told reporters in New Delhi.

An intelligence official said on the condition of anonymity because he is not authorized to speak to the media that the alert was sent to several “vulnerable” cities after some militant groups vowed revenge for the recent hanging of Afzal Guru, convicted for the attack on parliament.

A police officer in New Delhi said that a man arrested in October had confessed to being part of a team that reconnoitered by motorcycle in several parts of Hyderabad, including Dilsukhnagar. The officer spoke on the condition of anonymity because it was considered premature to link Thursday’s blasts with that arrest.

An intelligence official in the capital, who spoke anonymously in line with agency rules, said Hyderabad is considered a “sensitive target” because it has been the scene of terrorist attacks before. In August 2007, two powerful bomb blasts there killed 40 people.

More than 100 Muslims were rounded up after the 2007 explosions and kept in custody for many months. A court eventually ordered their release, citing a lack of concrete evidence of their role in the blasts.

The Hyderabad-based Civil Liberties Monitoring Committee appealed to the media Thursday to be “sensitive in reporting the blasts, [to] halt their self-investigation and [to] stop targeting a particular community” by quoting unnamed intelligence sources.”

A national security team was heading to Hyderabad to examine the type of explosives used, the Press Trust of India reported.

“This is a very congested area,” Sarve Satyanarayana, a member of Parliament from the Dilsukhnagar area, said in a telephone interview. “A lot of people gather there all the time. It is a commercial area. There is a bus depot, shops, eateries, one big temple and cinema halls.”

The lawmaker added: “Such attacks will spoil the image of our city. I don’t know who has committed this heinous crime.”