ROME (AP) — Italian police on Wednesday arrested 29 suspected smugglers as they smashed a transnational operation that for years brought migrants illegally into Italy by sea and then moved them overland to northern Europe, authorities said.

The nearly four-year-long investigation was spearheaded by prosecutors in Calabria, the “toe” of the Italian peninsula, where many of these migrants arrive from Turkey or Greece, often on well-outfitted sailboats that elude detection by police or military personnel.

Depending on how much the migrants could pay — investigators said some paid as much as 15,000 euros ($16,500) apiece just for the sea leg of the voyage — the passengers on the land routes to northern Europe either took trucks, trains or taxis across Italy's northern land borders. Transit points included Ventimiglia, an Italian city near its border with France and Trieste, in eastern Italy near Slovenia.

Police said colleagues in Turkey, Greece, Belgium, Germany, Sweden, Britain and Morocco collaborated in the investigation that led to the arrests. The operation began at dawn Wednesday in Italy when some 200 officers fanned out in various cities, including other major points on the smugglers' land routes, the cities of Milan and Turin.

From the moment the migrants set foot in southern Italy — either in Calabria or in Puglia, an adjacent region forming the “heel” of the peninsula — the smugglers looked after the travelers until they could be moved into northern Europe, according to written statements by the Italian police.

"In effect, a real and true system of illegal welcome, organized both abroad and in various Italian cities, that included food and lodging in the various stops, was created, and to which the migrants entrusted themselves completely,'' Francesco Messina, a top Italian police official, said in a statement.

The smugglers exploited a sea route plying the Mediterranean between Greece and Turkey and southern Italy and used sailboats — less likely to appear to be a migrant vessel than the frequently used overcrowded rubber dinghies or decrepit wooden fishing boats, according to the Italian authorities.

Those arrested risk being charged with aiding illegal immigration and money laundering in connection with some 30 sea voyages, police said. Many of the crew were from Ukraine or other former Soviet Union countries, while the ringleaders were mainly from Iraqi Kurdish areas, according to the Italian authorities.

Most of the passengers were of Asian or Middle Eastern origin, the police said.

It was an aging wooden boat, and not a sailboat, that capsized and splintered after smashing into a sandbank just off a Calabrian beach on Feb. 6, killing 92 migrants. Authorities said the smugglers aboard deliberately kept the boat for hours longer at sea, despite very high waves, in hopes of eluding detection by police ashore.

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