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Hundreds of migrants are feared to have drowned today after a fishing boat carrying them capsized in the Mediterranean Sea off the coast of northern Libya. Varying reports estimate that between 600-700 migrants were onboard the vessel when it flipped.

The boat was reportedly around 68 miles (110 kilometers) northwest of the Libyan capital of Tripoli. Irish and Italian officials were sent to rescue any survivors and said that at least 150 people were spotted in the sea.

Captain Donal Gallagher of the Irish navy said that the Irish vessel Le Niamh was one of several ships requested by the Italian coast guard to help with the rescue efforts. The Italian army also dropped additional life rafts via helicopter into the sea to help any stranded survivors stranded at sea.

The Italian and Irish vessels were there as part of the multi-million dollar border security operation conducted by Frontex, the European Union's border security agency.

Reports by the advocacy group Migrant Report indicate that "The Dignity", a rescue ship operated by Médecins Sans Frontières/Doctors Without Borders was also dispatched to the boat, which at the time was still afloat, and intercepted a rubber dinghy with 94 people on board.

Officials have yet to confirm what caused the boat to capsize.

According to official figures released by the International Organization of Migration on Tuesday, over 2,000 migrants have lost their lives in the Mediterranean since the beginning of 2015, in comparison with 3,279 deaths throughout the whole of last year.

The Associated Press contributed to this report.