A big blast in the Turkish capital, Ankara, has left 28 people dead and 61 wounded.
The explosion took place during rush hour on February 17 in an area close to where military headquarters and parliament are located.
Governor Mehmet Kiliclar said the bomb appeared to target a convoy of buses carrying military personnel.
Reports said several cars caught fire and dozens of ambulances rushed to the scene. Dark smoke could be seen billowing from far away.
Deputy Prime Minister Bekir Bozdag said the attack was an act of terrorism.
Prime Minister Ahmet Davutoglu, who had been due to leave for a trip to Brussels later on February 17, canceled the trip. Instead, he attended an emergency security meeting with President Recep Tayyip Erdogan and other senior officials.
The government also banned Turkish media from broadcasting or printing graphic images of the dead or injured from the scene of the explosion.
Similar bans have been imposed after previous attacks.
Suspicion on who was behind the bombing fell on several groups.
Kurdish militants, radical leftists, and Islamic radicals have all staged bombings in Turkey in recent years.
Erdogan said the attack exceeded all "moral and humane boundaries," and vowed to go after the "forces" behind the assailants.
The United States, NATO, and Germany voiced solidarity with Turkey over the tragedy.
"The United States strongly condemns the terrorist attack on Turkish military personnel and civilians," deputy State Department spokesman Mark Toner said.
"We reaffirm our strong partnership with our NATO ally Turkey in combating the shared threat of terrorism attacks."
German Chancellor Angela Merkel said: "We as Germans are sharing your pain.... In the battle against those responsible for these inhuman acts we are on the side of Turkey."
NATO Secretary-General Jens Stoltenberg said there can be no justification "for such horrific acts" and that "NATO allies stand shoulder to shoulder in the fight against terrorism."
Commentators say a central strategy of the outlawed Kurdistan Workers Party, which has waged a three-decade insurgency in Turkey, has been to attack military targets, although it has largely focused on the mainly Kurdish southeast.
The Turkish security forces have been engaged in large-scale operations against Kurdish militants in the southeast since December.
It's the second time in several months that Ankara has been the victim of a bomb attack.
In October, suicide bombings blamed on the Islamic State (IS) extremist group targeted a peace rally outside the main train station in Ankara, killing 102 people in Turkey's deadliest attack in years.
Militants have also targeted other sites in Turkey, which has been helping efforts led by the United States to combat IS in neighboring Syria.
Last month, 11 German tourists were killed after a suicide bomber affiliated with IS detonated a bomb in Istanbul's historic Sultanahmet district.
More than 30 people were killed in a suicide attack in the town of Suruc, near Turkey's border with Syria, in July.
With reporting by AP and Reuters