More than 1 million refugees have crossed into Europe this year, the International Organization for Migration said Tuesday, passing a symbolic milestone amid the fallout of war, poverty and persecution in Africa and the Middle East.

With just days left in 2015, the Geneva-based intergovernmental organization says the million mark was crossed Monday, marking more than a four-fold increase from last year.

IOM says more than 820,000 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.

The 162-country intergovernmental agency says the arrival of more than 4,100 people into Greece on Monday put the annual total over 1 million. The figure includes more than 34,000 arrivals by land from Turkey into neighboring Greece and Bulgaria, or only about 3.5 percent of the total this year.

Most of the 2,889 deaths this year came on the Mediterranean between north Africa and Italy, IOM said. Another 706 people are known to have died trying to cross the Aegean between the Turkish coast and a number of nearby Greek islands.

IOM says its figures are pulled together through a combination of people registered and thus counted, as well as estimates given the sheer numbers. The agency compiles figures provided by law enforcement in countries like Italy and Greece, and its own monitors carry out a real-time count on the Greek islands and in Italy.

The refugee crisis, Europe's worst since World War II, has forced European governments to scramble to cobble together a response, and caused rifts between EU member states.

Germany and Sweden have been among the most welcoming, while some less-wealthy eastern European countries have erected border fences in an attempt to block the flood of refugees.

Germany has seen around 1 million migrants arrive this year, but that figure includes large numbers of people from Balkan countries who arrived earlier in 2015.