ROME (Reuters) - An Italian judge on Friday cleared three migrant sea rescue charities that had been accused of abetting irregular immigration in complicity with human traffickers, throwing out a case opened more than seven years ago.

A pre-trial judge in Trapani, Sicily, said there were no grounds to proceed against international charities Doctors Without Borders (MSF), Save the Children and Germany's Jugend Rettet.

The decision is a vindication for the non-governmental organisations (NGOs) that had always denied any collusion with traffickers and rejected accusations from Italian politicians of acting as "sea taxis" for migrants.

"These unfounded accusations have attempted to tarnish the work of humanitarian search and rescue teams for years," said MSF's International President Christos Christou.

"They were intended to remove vessels from the sea and to counter their efforts of saving lives and bearing witness. Now these accusations have collapsed."

Italy is the first port of call for thousands of people who try to cross the Mediterranean from north Africa, and rescue charities have often been targeted by political parties pledging to stem the arrivals.

Right-wing Prime Minister Giorgia Meloni has accused the rescue NGOs of acting as "ferry boats" for migrants, and her government has passed legislation to curb their activities, including through the impounding of their vessels.

Elly Schlein, leader of the opposition Democratic Party, said Friday's ruling was "a historic sentence" that showed "solidarity is not a crime".

In 2017, Trapani prosecutors seized Jugend Rettet's rescue boat, the "Iuventa", saying they had found "serious evidence" of encounters at sea between its crew members and Libyan traffickers.

They launched similar charges against Save the Children and MSF, without impounding their vessels. Following the accusations, Jugend Rettet and Save the Children stopped Mediterranean sea rescues, while MSF continued them.

Italy faces a steady inflow of sea migrants from north Africa, but their numbers have fallen from a 2016 peak following border control deals with Libyan and Tunisian authorities.

In the year to date, around 16,000 migrants have arrived on Italian shores, compared to 35,000 in the same period of 2023.

NGO vessels are responsible for a small fraction of sea rescues in the central Mediterranean - about 4.2% of the total, according to Italian interior ministry statistics for the January-July 2023 period.

(Reporting by Alvise Armellini and Gavin Jones, editing by Barbara Lewis)