Turkish police have detained four people over a car bomb attack which killed five people and injured 68 in the south-eastern city of Diyarbakir.
There has been no claim of responsibility yet for the attack
The four are suspected of links to Thursday's bombing in the Kurdish-majority city, Turkish prosecutor Durdu Kavak said.
The bomb was set off remotely and targeted a military bus as it passed through the city centre, officials say.
Kurdish separatists have carried out bombings in the region before.
The blast on Thursday caused a huge blaze, igniting several vehicles.
Four of those who died were school students, Turkish officials said. At least 30 soldiers were among the injured.
Police said they suspected Kurdish militants. Diyarbakir is the biggest city in the mainly Kurdish south-east.
Speaking in the capital, Ankara, Prime Minister Recep Tayyip Erdogan condemned the blast as a "terrorist act".
Turkish troops are fighting Kurdistan Workers' Party (PKK) rebels both inside Turkey and in nearby northern Iraq. In December Turkish warplanes launched several strikes on PKK targets in northern Iraq.
Mr Erdogan said the "terrorist organisation has not been, and never will be, the representative of Turkish citizens of Kurdish origin".
He vowed that Turkey "will deal with this matter with determination and without making any concessions".
The European Union and United States also condemned the Diyarbakir bombing.
The EU presidency, held by Slovenia, called it an "atrocious act of terrorist violence" and expressed "full solidarity" with the Turkish people.
There have been a number of explosions in Diyarbakir in the past, the most recent of which was caused by a bomb at a bus stop in 2006.
Thursday's explosion happened during rush hour in an area close to a military residential complex and a helicopter base, reports say.
A correspondent for the BBC Turkish Service who was only about 70 metres away from the blast said there was an enormous explosion, which caused a number of vehicles to catch fire and windows to shatter.
"Our car shook violently, then we saw flames going up towards the sky," said Kadir Konuksever. "We ran towards the flames and saw injured people scattered all over. Their screams were unbearable.
"Fire crews arrived within four to five minutes, but the flames were such that they could not get to the injured either. They had to deal with the flames before tending to them."
Turkish television said the blast could be heard 3km (two miles) away.
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