At least five wounded in Mexico resort bar attack

Investigators believe the blast was intentional but were unable to confirm media reports it was caused by a grenade, a spokesman for the prosecutor's office said on Thursday.

As many as 15 people were injured in the attack, including four who lost limbs, Mexican media said.

Puerto Vallarta is a popular Pacific coast destination for sun-seeking foreign tourists. It was not known if any foreign tourists were among the approximately 100 people in the bar when the attack occurred.

No motive for the attack was known.

Violence in Jalisco, where Puerto Vallarta is located, has increased since security forces killed top drug trafficker Ignacio "Nacho" Coronel, who controlled the drug trade in the state, in July.

More than 28,000 people have died in escalating drug violence since President Felipe Calderon launched his war on drugs in late 2006, but tourists are almost never targeted.

The Puerto Vallarta attack came a day after the grisly discovery of the bodies of 72 people thought to be migrant workers in an empty building on a remote ranch in northern Mexico.

(Reporting by Robert Campbell; Editing by Jerry Norton)