A local armed group in a Libyan coastal city west of the capital Tripoli has reportedly been halting refugee boats from setting out across the Mediterranean, leading to a rapid drop in the risky sea voyage over the past month.

The revelation sheds a new light into the sudden decline in the number of asylum seekers arriving in Italy, Reuters reported Monday citing multiple local sources in the city of Sabratha in Libya’s Zawiya district who spoke on condition of anonymity.

According to the report, arrivals of refugees in Italy from North Africa -- the main route for migration to Europe this year -- fell by more than 50 percent in July compared to the same period last year, and August arrivals so far are down even further.

July and August are peak months for people smugglers operating the substandard boats to carry refugees to Europe due to favorable sea conditions.

Sources cited in the report stated that the sudden drop in the refugee flow had been caused by a new militia in the seaside city -- 70 kilometers west of Tripoli -- which is blocking the asylum seekers from leaving, often by detaining and holding them in custody.

The militia force in Sabratha "works on the ground, the beach, to prevent the migrants leaving on boats towards Italy," said an unidentified “civil society organizer” in the city, as quoted in the report, noting that the group is made up of several hundred "civilians, policemen, army figures."

It further quoted a second source in the city – “who follows smuggling activity closely” -- as saying that the force is conducting a "very strong campaign" that was launched by a "former mafia boss."

The report then cited yet another source “with contacts in Libya” as saying that the Sabratha group was making "a significant effort to police the area."

The sources further asserted that the armed militia force was also operating a detention center for refugees who are turned back or seized from smugglers, and one sent a photo of hundreds of asylum seekers sitting in the sand in front of a high wall.

According to one of the sources cited in the report, the group appeared to be seeking legitimacy and financial support from Tripoli, where European states have tried to partner with a UN-backed Government of National Accord (GNA) to curtail the refugee flows.

However, it was not possible to make contact with the group, known as Brigade 48, according to one of the sources.

The development came as Italy has been making efforts to boost GNA's ability to contain people smuggling with cash, training and by sending a ship to help repair Tripoli's coastguard and navy vessels.

Italy, the report says, wants to replicate a deal with Libya that the EU struck with Turkey last year, largely shutting down the refugee route through Greece and the Balkans.

With an upcoming national election in the first half of next year, the Italian government is under pressure to demonstrate that it can halt, or at least trim down refugee in-flow.

An estimated 600,000 asylum seekers have reached Italy by sea from North Africa since 2014, and more than 12,000 have drowned while trying.