The International Organization for Migration says the million mark was crossed Monday - marking more than a four-fold increase in comparison with last year. The actual number of arrivals recorded as having entered the continent by December 21 was 1,005,504. The Geneva-based group says says more than 800,000 crossed into Greece from Turkey, including more than 455,000 from Syria and over 186,000 from Afghanistan. Nearly 3,700 others died trying to cross the Mediterranean amid Europe's worst refugee crisis since World War II, it added Germany has seen around one million migrants arrive this year, but that figure includes large numbers of people from Balkan countries who arrived earlier in 2015. The vast majority of the arrivals from outside Europe have used the so-called Balkan corridor - a route that takes migrants from Greece, through Macedonia, Serbia, and then either Croatia and Slovenia or Hungary to Austria and Germany. The UN's refugee agency urged Hungary on Monday to end policies that promote "intolerance and hatred" after the country built a huge fence along its southern border to keep migrants out.