Twin explosions hit a train station in Ankara on Saturday where several unions, civic society organizations and pro-Kurdish People’s Democracy Party were due to hold a rally.
The gathering was aimed at protesting against conflict between the state and Kurdish militants in southeast Turkey.
95 people are confirmed dead, and 246 others wounded.
No group has claimed responsibility.
Turkish President Recep Tayip Erdogan condemned the attack, which he said targeted the unity of the country.
The Turkish government declared a three-day mourning to commemorate victims of the blasts.
Prime Minister Ahmet Davutoglu promised that authorities will find the perpetrators of the attack.
The blasts also drew condemnation elsewhere in the world.
UN chief Ban Ki-Moon says he expects the “perpetrators of these terrorist acts to be swiftly brought to justice.”
The White House says President Obama “conveyed his deepest personal sympathies” for the victims and condemned in the strongest terms the horrific attacks.
Meanwhile, Russian President Vladimir Putin urged the international community to unite anti-terrorism efforts as he expressed condolences to families of the victims.
SOUNDBITE (RUSSIAN): VLADIMIR PUTIN, Russian President
“We should consolidate our efforts in a fight against this evil. What happened in Turkey, is an attempt to destabilise the situation in a neighboring and friendly country for us. Moreover, it was done in the course of an election campaign. This is an obvious provocation.”
Ankara is set to hold snap elections on Nov. 1, amid increased tension and polarization among major political parties that failed to form a coalition government after elections in June.
Turkey resumed an offensive against the outlawed Kurdish Workers’ Party in late July after two policemen were killed by the terrorist group.
Violence has since escalated sharply, with the PKK stepping up attacks on security forces. More than 100 members of Turkish security personnel have been killed in clashes.