The wall of silence that has shielded Europe's most powerful, but most shadowy, organised crime group is finally set to fall, with the assistance of a pair of "supergrasses" who have turned against their former allies.

Following 15 years in which Calabria's 'Ndrangheta mafia appeared impervious to any attempts to infiltrate it, Italian investigators say the state now has not one but two informants – a development that has shaken the organisation to the core.

High-ranking mobster Antonino Lo Giudice has begun talking to investigators in the past few days. His evidence comes just a month after another key 'Ndrangheta figure, Roberto Moio, began revealing the shadowy group's secrets.

The 'Ndrangheta, which has an estimated £40bn turnover thanks to its dominant role in Europe's cocaine trade, is tighter-knit than Sicily's Cosa Nostra. Its exceptionally strict code of silence has, at least until now, proved its greatest strength.

In desperation at new developments, however 'Ndrangheta leaders have launched what one leading Italian journalist specialised in organised crime, Attilio Bolzoni, has described as a "war on the state", with a string of bomb blasts targeting leading prosecutors and Reggio Calabria's main courthouse.

On 5 October an anonymous caller told police to look near the city's anti-mafia HQ for "a surprise" for the regional prosecutor, Giuseppe Pignatone. Under an old mattress dumped in the street, they found a bazooka rocket launcher. Mr Pignatone had previously received a letter containing three bullets. In late August, a bomb had damaged the entrance to the city-centre home of the Reggio Calabria region's prosecutor general, Salvatore Di Landro, blowing out windows in the vicinity.

Rome responded by sending troops into the southern Calabrian region earlier this month, at the request of local authorities.

On Saturday it emerged that Italy's Justice Minister, Angelino Alfano, has recently received death threats. "The clans of the 'Ndrangheta have to understand that the state is present and will win," he responded.

While welcoming the new willingness to tackle organised crime, critics have noted that the state's failure to intervene in recent decades has allowed the phenomenon to grow. The power of the 'Ndrangheta has become so pervasive in its home region, and some towns so thoroughly corrupted, that Rome has installed emergency commissions in place of local councils.

But Mr Bolzoni wrote in La Repubblica newspaper recently that the tide is turning, thanks to the new informants – and the new wave of magistrates and special police units sent into the region, which enabled those witnesses to be seized in the first place. Of the two mobsters-turned witnesses, Mr Bolzoni said that Moio, a 'Ndrangheta colonel and a member of the feared Tegano clan, was in the position "to reveal nearly 20 years of secrets".

Reggio Prefect Luigi Varratta agreed that confirmed 'Ndrangheta bosses were worried: "The extraordinary work of judges and police is bothering the clans. The mafiosi are keyed up, and reacting nervously."

Prosecutors are still deciding whether Lo Giudice can be admitted to Italy's witness protection programme; but already on the basis of one of his first tip-offs the police located a weapons cache that included 11 Kalashnikovs.

Italian investigators received another boost in July this year when they captured Domenico Oppedisano, who had recently been revealed as the organisation's "boss of bosses". Oppedisano, 80, was foundhiding in a small coastal town in Calabria. The existence of a supreme boss indicated that, contrary to previous intelligence, the Calabrian crime group has a pyramidal structure similar to that of the Sicilian mafia. This would leave it more vulnerable to key arrests.