Gunmen in Cancun, Mexico attacked the state prosecutors' office on Tuesday, killing four. According to one witness, the gunmen threw two explosive devices at a wall before shooting the officers.
The attack comes just one day after a similar shooting attack at music festival held in a nearby town killed three foreigners and two Mexicans.
Governor of Quintana Roo State Carlos Joaquin said the federal government was sending more police to reinforce security in the region.
Quintana Roo Attorney General Miguel Angel Pech said authorities were investigating whether extrortion, a murder plot, or street-level drug sales were behind the Tuesday shooting in nearby Playa del Carmen.
Authorities suspect Tuesday's attack, which killed 5 and wounded 15, is linked to drug-dealing Zetas cartels in nearby Playa del Carmen.
"Either they didn't reach an agreement over protection payments - extortion - or it may be that somebody did not allow them to sell drugs inside the nightclub," Pech said. "Perhaps the strongest hypothesis is that this person had gone there to demand they comply with protection payments."