Turkey has vowed to retaliate against the perpetrators of a powerful blast in the capital Ankara that left at least 28 people dead and 61 injured.
"Turkey will not shy away from using its right to self-defence at any time, any place or any occasion," President Recep Tayyip Erdogan said.
Officials said a vehicle full of explosives was detonated as military buses were passing by on Wednesday.
Funerals are expected to take place later on Thursday.
No group has so far said it was behind the attack.
The US condemned the blast, with National Security Council spokesman Ned Price saying: "We stand together with Turkey, a Nato ally, a strong partner."
The blast happened in an area close to parliament and military headquarters.
Large plumes of smoke were seen rising from the area and witnesses said the blast was heard all over the city.
Some of the victims were civilians.
In a separate development later on Wednesday, an explosion damaged a building housing a Turkish cultural centre near the Swedish capital Stockholm, officials said. No-one was injured. It happened in Fittja, where a man was shot dead a few days ago after attending a pro-Kurdish rally.
In a statement released several hours after the Ankara attack, President Erdogan said: "Our determination to retaliate to these attacks, in Turkey and abroad, which aim at our unity, togetherness and future, is increasing with such actions."
Mr Erdogan cancelled a planned trip to Azerbaijan on Thursday, while Prime Minister Ahmet Davutoglu also said he would not go to Brussels where he was due to attend meetings about the refugee crisis in Europe.
Meanwhile, Deputy Prime Minister Bekir Bozdag described the attack, which happened at about 16:30 GMT (18:30 local time), as an "act of terrorism".
Security forces carried out a controlled explosion on a suspect package after the blast.
Turkey has been hit by a series of attacks in recent months, and there have been increasing concerns that the country could be targeted by another big attack.
It is not clear who was behind the blast in Ankara. Security sources blamed both so-called Islamic State (IS) and militants from the banned Kurdistan Workers Party (PKK), Reuters reported.
A government spokesman said the attack had been well planned.
Recent attacks in Turkey
- January 2016: At least 10 people, mostly German tourists, are killed in a suspected IS suicide bombing in Istanbul
- October 2015: More than a hundred people are killed in a double-suicide bombing at a Kurdish peace rally in Ankara
- July 2015: In the predominantly Kurdish town of Suruc, near the Syrian border, over 30 people are killed in a suicide bombing, again blamed on IS
The PKK has been fighting for autonomy for Turkey's Kurdish minority for decades and has carried out regular attacks on Turkish security forces.
The blast in Ankara comes as Turkey steps up its involvement in the conflict in neighbouring Syria.
It has been shelling the Kurdish YPG militia in northern Syria, who it sees as allied to the PKK.
Turkey has also allowed a US-led coalition bombing IS to use one of its air bases.