Twin explosions outside the main train station in the Turkish capital Ankara killed at least 95 people and wounded hundreds of others at a peace rally on Saturday, in what government officials described as a terrorist attack.
Authorities were investigating claims the attacks were carried out by a suicide bomber, two government officials told Reuters. Prime Minister Ahmet Davutoglu was due to hold an emergency meeting with the heads of the police and intelligence agencies and other senior officials, his office said.
Turkey's government says it has imposed a temporary news blackout following the attack, Turkey's deadliest in recent years.
A government spokesman said the blackout Saturday covered images showing the moment of the blast, gruesome or bloody images or "images that create a feeling of panic."
He warned media organizations they could face a "full blackout" if they did not comply.
On Saturday, many people in Ankara reported being unable to access Twitter and other social media websites after the blasts. It was not clear if authorities had blocked access to the websites.
Turkey frequently imposes blackouts following attacks.
Witnesses said the two explosions happened seconds apart shortly after 10:00am (0700 GMT) as hundreds gathered for a planned "peace" march to protest against the conflict between Turkish security forces and Kurdish militants in the southeast.
Violence between the state and the Kurdistan Workers Party (PKK) militants has flared since July, when Turkey launched air strikes on militant camps in response to what it said were rising attacks on the security forces. Hundredshave since died.
Those involved in the peace march tended to the wounded lying on the ground,as hundreds of stunned people wandered around the streets. Bodies lay in two circles around 20 metres apart where the explosions had taken place.
The attacks come three weeks ahead of a parliamentary election in Turkey and at a time of multiple security threats, not only in the restive southeast but also from Islamic State militants in neighbouring Syria and home-grown leftist militants.
The NATO member has been in a heightened state of alert since starting a"synchronized war on terror" in July, including air strikes against Islamic State fighters in Syria and PKK bases in northern Iraq. It has alsorounded up hundreds of suspected militants at home.
Designated a terrorist group by Turkey, the United States and the European Union, the PKK launched a separatist insurgency in 1984 in which more than 40,000 people have been killed.
The state launched peace talks with the PKK's jailed leader in 2012 and the latest in a series of ceasefires had been holding until the violence flared again in July.
--The Associated Press and CNBC.com contributed to this article.