"At present, six people who were injured directly by the grenade explosion are hospitalised in Caucasia; 18 more are in El Bagre hospital and their injuries were inflicted by the shattered glass of the drinks that they had been drinking at the party," Blu Radio broadcasted the head of Antioquia police Carlos Sierra as saying.
Casualty reports vary, with local media reporting the toll to be ranging from 25 to 29.
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The explosion occurred after two men on a motorcycle reportedly threw a grenade inside the nightclub.
Authorities suspect the Clan del Golfo paramilitary organisation and the Caparrapos armed gang to be behind the attack.