San Juan, Puerto Rico  - An attack on a bar in Puerto Rico left eight people dead and 20 other injured, local media reported Sunday.

Two attackers opened fire in the La Tombola bar in Toa Baja on the Caribbean island's north coast shortly before midnight Saturday, El Nuevo Dia newspaper said.

An eight-month pregnant woman was among those shot, killing the baby in her womb. The woman was in critical condition in hospital.

The motive for the attack remained unclear, but local media said it may have been drug related with the recent arrest of drug boss Angel M Ayala Vazquez sparking a possible a drug gang war.

The US territory of Puerto Rico is home to about 4 million residents. (dpa)