At least 17 people are dead and 56 are in hospital after using what is thought to have been poisoned cocaine.
The cases are clustered around several towns in Buenos Aires province, Argentina’s most populous.
Samples of the drug are being analysed but judicial officials said the most popular theory was that the cocaine was deliberately tampered with as part of a settling of scores between traffickers.
The dead are from the towns of Hurlingham, San Martin, and Tres De Febrero, but authorities have warned the death toll could rise.
