MEXICO CITY – At least 20 people were wounded, four of them seriously, when unidentified individuals tossed a bomb into a bar in Puerto Vallarta, a resort city on Mexico’s Pacific coast, police said Thursday.

The attack occurred around midnight Wednesday at the Pink Cheladas bar, where about 150 young people were partying, Puerto Vallarta police department spokesmen told Efe.

The majority of the victims are in their 20s and one is 35.

Two of the victims had to have limbs amputated, while a third has an exposed leg fracture.

The press reported that a grenade was used in the attack, but the police spokesmen said investigators had not yet determined whether the assailants used a grenade or a Molotov cocktail.

The army and navy are trying to identify the type of weapon used in the attack in Puerto Vallarta, which is in Jalisco state.

The assailants threw the bomb “inside the bar” and “it exploded nearly in the middle” of the establishment, police department spokesmen said.

Five bomb threats had been received this year by different establishments in Puerto Vallarta, with the latest coming early Saturday, but no attacks had taken place.

No threats were received at the Pink Cheladas bar before the attack, police said.

No arrests have been made, but investigators have taken statements from most of the injured and the investigation is “at an advanced stage,” police said. EFE