Judicial sources said the explosion at a rally of the pro-Kurdish People's Democratic Party (HDP) in southeastern city of Diyarbakir was caused by a cylinder bomb packed with hundreds of ball bearings.
The ruling Justice and Development Party (AKP) wants to take a large majority in tomorrow's legislative elections and change the constitution to give Turkey's charismatic but divisive President Recep Tayyip Erdogan more power.
But polls have indicated that its vote could be well down on the almost 50 percent score the AKP reaped in the last elections in 2011 and may even need to form a coalition.
But judicial sources in Diyarbakir told AFP that investigators had confirmed that the explosion was caused by a bomb.
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"The experts collected hundreds of ball bearings and pieces of the metal cylinder," said a source, who asked not to be named.
The source confirmed that no suspect had yet been arrested over the blast but fingerprint and video evidence had been found.
In a statement, Diyarbakir prosecutors confirmed that two people had been killed and over 100 wounded.