The number of casualties announced late Saturday by the prime minster's officer was lower than the figures given earlier by the Turkish Medical Association. That agency said 97 people had died and more than 400 were wounded. The prime minster's office said 48 victims were in intensive care.
The reason for the lower casualty figures wasn't clear.
The explosions happened during a peace march involving, among others, the pro-Kurdish HDP, or People's Democratic Party.
Most of the victims were attending a lunchtime demonstration calling for an end to the renewed conflict between the Kurdistan Workers' Party (PKK) and the Turkish government.
About 14,000 people were in the area. Two suicide bombers are believed to have caused the blasts, Turkish Prime Minister Ahmet Davutoglu said in a televised address to the nation.
"In total 97 people have been murdered, 68 of them died right after the blast, whereas 29 of them were severely wounded and sent to the hospitals, where they lost their lives," said Dr. Huseyin Demirdezen, a member of head council of Turkish Medical Association.
The attack came three weeks before national elections.
A video on social media shows a ring of young people dancing and singing before an orange blast erupts in the background. The video ends with the crowd running away from the blast.
Following the attack, for which no group has claimed responsibility, bodies lay in front of the station on Hipodrum Street and bystanders and paramedics tended to the wounded as a police helicopter circled overhead.
Video showed protest banners and flags littering the ground. Members of the public helped carry the victims to ambulances and buses to take them to hospitals.
The blasts were so powerful they shook high-rise office buildings. The death toll is expected to climb.
A newly aggressive stance toward ISIS
Suspicion immediately fell on either the ISIS terrorist group or Kurdish separatists in Turkey.
Davutoglu called for three days of national mourning and urged the country to fight terrorism.
"This is an attack that does not target a specific group; it is an attack on the entire nation and (an) attack on our unity. Turkey is a country that has managed to maintain peace in the region," he said.
Davutoglu said Turkey was warned about suicide bomb attacks and in the past three days arrested two suspects.
Turkey has avoided conflict with ISIS, perhaps in exchange for the release earlier this year of dozens of Turkish hostages seized in the Iraqi city of Mosul. The quid pro quo of that deal has never been announced.
However, Turkey recently changed its stance and allowed the U.S. to launch strikes
on ISIS from Incirlik Air Base in southern Turkey.
The U.S. condemned the attack and urged Turkish citizens to "recommit to peace and stand together against terror," State Department spokesman John Kirby said in a statement.
President Barack Obama spoke with Turkish President Recep Tayyip Erdogan and "conveyed his deepest personal sympathies for those killed and injured in these heinous attacks, and affirmed that the American people stand in solidarity with the people of Turkey in the fight against terrorism and shared security challenges in the region," according to a White House statement.
CNN national security analyst Peter Bergen said there was nothing about the attack that would point to one group over another as being responsible.
"I think that from what we know, it appears to have been a suicide bomber," Bergen said. "Both groups have deployed these in the past.
"I will say that when we've seen ISIS attacks, they have tended to be in the border region along the Turkish/Syrian border. This is of course in the capital, Ankara, in the middle of the country, so that's something to think about. And again, go back to the context of this rally. It was at a rally to protest the war by the Turkish state and Kurdish separatists."
Is Turkey hurting ISIS?
But some observers had predicted Turkey might be subject to terrorist attacks because of its newly aggressive stance toward ISIS.
In an interview with CNN in July
, Esra Ozyurek, chair of Contemporary Turkish Studies at the London School of Economics, said that attacks in Turkey, or the absence of them, would indicate whether ISIS was being hurt by the strikes originating from Turkey.
"If Turkey's really hurting ISIS, then there will be attacks," Ozyurek said.
Many Turks have joined ISIS' ranks, with a large number being recruited in Ankara, according to reports. Turks may make up a third of ISIS, according to reports.
But, on the Kurdish front, a peace process last year appeared close to reaching an agreement.
However, when Erdogan's party failed to win many votes
in Kurdish areas of the country in June, he appeared to abandon the reconciliation process.
In return, hostilities between Kurds and the Turkish government, which have killed tens of thousands of people since 1984, have been renewed.