Story Highlights• NEW: Prime minister calls the rush-hour blast a terror bombing
• Death toll rises to 5 in explosion in Turkish capital, officials say
• Dozens more hurt by blast in historic neighborhood of Ankara Tuesday
• Initially police said explosion was an accident; now believed to be a bomb
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ANKARA, Turkey (CNN) -- A powerful blast believed to be a bomb ripped through an Ankara shopping district Tuesday, killing at least five people and wounding dozens more.
Anti-terror squad police at the scene said they have found traces of A4 plastic explosives.
The rush-hour explosion went off in a busy shopping area of the city -- Ulus -- and during an international defense fair, where companies show their wares to militaries.
Investigators are trying to determine whether the bomb was planted or was detonated by a suicide attacker, according to Prime Minister Recep Tayyip Erdogan.
Erdogan called the blast a terror bombing and said the "unfortunate event" occurred despite "very heavy precautions" against such attacks. (Watch as ambulances rush to the scene of the deadly blast )
"We have to unite against terrorism," he said. "We have to create a global platform against terrorism."
Police said A4 explosive is often used by militants in the radical separatist Kurdistan Workers Party -- known by its Turkish initials, PKK. Its fighters have been staging attacks against Turkey in the country's southeast and from the Kurdish region of neighboring Iraq.
Police are also trying to track down a red vehicle that was at the scene.
Erdogan confirmed five deaths to news reporters. One of the dead was a Pakistani and the others were Turks.
Four of the more than 60 people injured were Pakistanis as well, Erdogan said.
The blast went off at the entrance of a seven-story shopping center, according to a CNN Turk journalist. That location is near a bus station, and the area is known for its tourist sites and bazaars.
News video showed covered bodies and bloody, injured people, some being carried onto stretchers. Witnesses described seeing body parts. Debris was scattered around the scene, and windows were knocked out of the building.
Investigators were searching the rubble for clues. Initially, authorities thought the blast was the result of an accident.
Dozens were killed in 2003 when militants bombed two synagogues, the British consulate and a bank in Istanbul, the country's largest city. There have been other bombing attacks as well, claimed by Islamic militants and Kurdish radicals.
Turkey is a secular country that is predominantly Muslim.
There has been a lot of tension in the country between secularist and traditional Muslims, and the state has been battling Kurdish separatists for many years.
Journalist Gokhan Eren contributed to this report.