The blasts were on the eve of deliberations in a court case that will determine the future of Turkish Prime Minister Recep Tayyip Erdogan's Justice and Development (AK) Party.
Turkish security officials say the first of two explosions that rocked the Gungoren district of Istanbul was a small explosive device placed in a trash can.
The first blast caused injuries but reportedly did not kill anyone. However, about 10 minutes later -- as a crowd gathered and emergency workers tended to the wounded -- a second, larger bomb was detonated in another trash can nearby.
Istanbul Governor Muammer Guler says it was the second explosion that killed at least 17 people and raised the injured toll to more than 150.
Authorities say they have no doubt that the double bombing was a terrorist attack. But they say it is too early to determine who was responsible.
In the past, bombings have been carried out in Istanbul by Kurdish separatists from the outlawed Kurdistan Workers Party (PKK), as well as by far-left groups and Islamist extremists.
Hashem Khosroshahi, an Istanbul-based political analyst, told Radio Farda today that he also thinks it is too early to reach any definitive conclusions about who carried out the attack. He says there are many different groups with different agendas that could have been involved.
The timing of the attack has focused media attention on Constitutional Court deliberations that began today in Ankara on whether Turkish Prime Minister Erdogan's (AK) Party should be banned from politics.
Erdogan's party won a decisive victory in legislative elections just one year ago. But with its roots in a banned Islamist party, it stands accused of violating the principle of secularism that is enshrined in the Turkish Constitution.
The Constitutional Court will deliberate on whether Erdogan's party has engaged in Islamist activities. That is expected to impact the decision on whether the party should be banned.
Huseying Bacgi, a political science professor at the Middle East Technical University in Ankara, has closely followed the case. He says he does not expect Erdogan's party to be banned.
"Most probably the party is not going to be closed down. But there will be some penalties or some financial fines. At the same time, maybe some politicians will be banned from political activities for the next couple of years," Bacgi says.
Still, Turkey has been plunged into political and economic uncertainty by the possibility that the ruling party could be banned.
Police also have been widening an investigation into a suspected ultranationalist group accused of seeking to overthrow the government. So far, 86 people have been arrested in that case.
Meanwhile, Turkey's military continues to be active in a campaign against Kurdish separatists in the southeast. It said earlier on July 27 that Turkish fighter jets had targeted and killed 12 suspected militants.
Radio Farda's Shabnan Nourian contributed to this report