ISTANBUL (Reuters) - Eighteen people were killed and 45 injured by an explosion in the administrative heart of Turkey's capital of Ankara on Wednesday, an interior ministry official told Reuters.
A vehicle laden with explosives detonated as military buses passed near the armed forces' headquarters, parliament and government buildings during the height of evening rush hour in an attack the Turkish military said was an act of terrorism.
Reports say initial signs indicate that militants from Turkey's outlawed Kurdistan Workers Party (PKK) were behind the Ankara bombing, a Turkish security source said.
However, separate security sources in Turkey's mainly Kurdish southeast gave a different account, saying they believed Islamic State militants were behind the bombing.
"I heard a huge explosion. There was smoke and a really strong smell even though we were blocks away," a Reuters witness said. "We could immediately hear ambulance and police car sirens rushing to the scene."
Turkish media reports said many people were injured. A health ministry official said the authorities were still trying to determine the number of dead and wounded, who had been taken to several hospitals in the area.
Images on social media showed the charred wreckage of at least two buses and a car. The explosion sent a large plume of smoke above central Ankara.
Turkey, a NATO member, faces multiple security threats. It is part of a U.S.-led coalition fighting Islamic State in neighboring Syria and Iraq, and has been shelling Kurdish militia fighters in northern Syria in recent days.
It has also been battling militants in its own southeast from the Kurdistan Workers Party (PKK), who have fought a three-decade insurgency for Kurdish autonomy. The PKK has frequently attacked military targets in the past, although it has largely focused on the mainly Kurdish southeast.
Wednesday's bombing comes after an attack in Ankara in October blamed on Islamic State, when two suicide bombers struck a rally of pro-Kurdish and labor activists outside the capital's main train station, killing more than 100 people.
A suicide bombing in the historic heart of Istanbul in January, also blamed on Islamic State, killed 10 German tourists.
COMPILED from various reports.