The tragedy has prompted widespread calls for emergency talks on the immigration crisis in Europe and for urgent investment in disaster-prevention efforts.
The International Organization for Migration's Director-General, William Lacy Swing, also said in a statement Sunday that Europe and other countries needed to act.
"The world needs to react with the conviction with which it eliminated piracy off the coast of Somalia a few years ago," Swing said in a statement on the IOM's website.
"All of us, especially the EU and the world's powers, can no longer sit on the sidelines watching while this tragedy unfolds in slow motion and well over 1,500 have drowned since the beginning of January."
In 2014, the IOM published a study in which it estimated that up to 3,072 would-be migrants died in the Mediterranean last year, compared with an estimate of 700 in 2013.
On Monday, there were media reports of another boat in distress on the Mediterranean with more than 300 migrants on board and around 20 fatalities.
The large increase in deaths recently has largely been driven by a surge in the number of fatalities in the Mediterranean region, the IOM said, although migration and its risks are not new to the region.
Since 2000, over 22,000 migrants have lost their lives trying to reach Europe, the body estimated, with conflict, persecution and poverty in northern Africa and the Middle East, in countries like Syria, key drivers of migration attempts.
Over 112,000 irregular migrants were detected by Italian authorities in the first eight months of 2014, almost three times as many as in all of 2013.