ANKARA - A powerful bomb outside a crowded shopping mall in the heart of Turkey's capital Ankara killed six people and injured 80 others on Tuesday local time, authorities said.
It was believed to be the worst in at least a decade to strike near Turkey's power centre, which houses the influential armed forces, the presidency and the government.
"We have seen a vicious, ruthless terror attack at Ankara's busiest time," Prime Tayyip Erdogan told reporters at the scene of the blast in the city's historic Ulus district.
There was no immediate claim of responsibility but a security source said all eyes were on separatist Kurdish rebels in the volatile southeast and Turkey's military chief said he feared similar blasts could hit other large cities.
Analysts said the blast was certain to raise tension ahead of July general elections, a contest fraught with strain between Turkey's secularist elite, the ruling Islamist-rooted AK party and Kurdish factions who accuse Erdogan's government of sidelining their candidates.
Erdogan said four Turks and one Pakistani were killed in the rush hour blast. State-run news agency Anatolian later said a sixth person had died in hospital and that six Pakistanis were also among the wounded.
Anatolian also reported Foreign Minister Abdullah Gul as saying that no Pakistanis were among the dead.
Turkish broadcasters CNN Turk and NTV said police were studying whether the bomb was placed in a package by a bus stop or if it was the work of a suicide bomber.
A security source, who declined to be named, told Reuters the government suspected the Kurdistan Workers Party (PKK) -- which is waging an armed struggle for greater Kurdish rights -- as the bombing bore the hallmarks of the rebels.
Parts of the mall's entrance collapsed, shop windows were blown out, debris was strewn across the street and police cordoned off the area as rescue workers carried injured people, many covered in blood, to ambulances.
"This is the most horrific scene I have ever seen. It gives me great grief," Ankara Mayor Melih Gokcek said.
More than an hour after the blast, three bodies, badly mutilated, laid in the street in front of the 5-storey building long after the blast occurred, a Reuters witness said.
At a prosecutor's request, an Ankara court imposed a ban on broadcasters and newspapers carrying footage or pictures of the bombing for the sake of the investigation and subsequent prosecution, Anatolian said.
Mehmet Yilmaz, a shop owner in the area of the blast, told Turkish television he saw someone on fire and tried to put out the flames by covering him with rugs and water.
"People were running away... I saw a few wounded people ... they were in shock and could not speak. I brought one of them to hospital," Harun Kiraz, a 42-year-old taxi driver, told Reuters.
Turkish media said the injured Pakistanis were in Ankara for a defence industry fair organised by the Turkish armed forces.
Police officers at the scene said A-4 plastic explosives were believed to the cause of the blast. A-4 is among the preferred explosives used by the outlawed PKK.
Police have detained seven people in connection with the bomb, Turkish broadcaster NTV said.
"This is an explosion by an organised terror group," armed forces Chief of General Staff General Yasar Buyukanit said after visiting the site. "You can expect this in any big city now."
The PKK ended a unilateral ceasefire on May 18 and security experts had expected attacks to escalate as a result.
Senior PKK commander Murat Karayilan has blamed Turkish intelligence for recent explosions in the northern Iraqi city of Arbil and said similar blasts would occur in heart of Ankara.
The PKK has been fighting for an ethnic homeland in a campaign of bombings, kidnappings and armed attacks since 1984, and Ankara blames it for more than 30,000 deaths.
"We must work together against terror in all countries of the world. We see the results of it in America, Britain, Spain, Italy and all places," Erdogan said.
Kurdish separatists, leftist militants and hardline Islamists have all launched bomb attacks in Turkey in the past.
Tuesday's explosion comes amid heightened political tension in European Union-applicant Turkey.
Erdogan's Islamist-rooted government has called a national election ahead of schedule to resolve a conflict with the secularist elite over a recent presidential election.
The secular establishment, including the military, judges and opposition parties, derailed the government's plan to elect Foreign Minister Abdullah Gul as president, fearing he might weaken the official separation of religion and state.