The explosion is thought to have occurred on a motorbike parked near the office of the Bharatiya Janata Party, a national opposition party that holds power in the local state of Karnataka.
"Preliminarily, we felt earlier that it was a (gas) cylinder blast as two vehicles that were on both sides of the motorbike got burnt," Bangalore police commissioner R Auradakar told reporters.
"As the motorcycle is fully burnt, we feel that it could be a blast."
A total of 12 people were injured, including eight policemen, he said.
Karnataka is to hold elections for its state assembly next month.
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