MILAN -- Officials in the southern Italian region of Puglia on Thursday demanded a more concerted response to Italy's long-underestimated "fourth mafia" after gunmen killed four people in an ambush, including two apparent bystanders who witnessed the hit.

The president of the Foggia province of Puglia, where the shootings occurred near an abandoned railway station, is calling for more uniformed law enforcement and more highly trained investigators to combat the Foggia crime syndicate, which is blamed for 17 killings this year alone.

"I am deeply shocked by the ferocity of the mafia ambush," Foggia president Francesco Miglio said before an emergency meeting of law enforcement led by Italy's interior minister later Thursday. "The barbarity even hit two innocent workers who were silenced only because they happened to be present for the crime."

A local crime boss appears to have been the main target when gunman travelling in a car opened fire on another vehicle, killing the boss and his driver, who was identified as his brother-in-law. The killers then chased down another vehicle with two residents who apparently happened to witness the hit, killing them.

Investigators said they were trying to understand if the attack was the result of a vendetta between clans feuding over territory, or if it is a skirmish in a wider mafia war.

The ambush has put the spotlight on a long-overlooked crime syndicate that authorities say arrived in Foggia, the spur of the Italian boot, decades ago as an offshoot of the Neapolitan Camorra, expanding from asserting control in agriculture to tourism and the drug route from Albania. Yet it never garnered national media attention like that of the Sicilian Cosa Nostra, the powerful Calabrian 'Ndrangheta or the Camorra itself.

"This extremely barbarous form of criminality in Foggia has been too long considered a second-class mafia," a top anti-mafia prosecutor, Franco Roberti, told RAI state radio. He said it has linked to 300 murders over the last three decades, 80 per cent unsolved.

Anti-mafia investigators said in a recent report that the Foggia organized crime syndicate had two main groups, one on the Gargano peninsula and the other inland, and was considered one of the most dangerous in Italy for the number of unsolved killings and the pervasive climate of "omerta," an unwritten rule of silence, among the population.

"The Foggia mafia is particularly ruthless and impenetrable, operating on primordial level," Roberti told the Turin daily La Stampa. "As we have seen in the recent dramatic episode, it is decidedly more violent and aggressive than the more organized mafias like the 'Ndrangheta, Cosa Nostra and Camorra."