(CNN) The number of migrants who have entered Europe by sea and land this year has passed 1 million, the International Organization for Migration said Tuesday.

It said that as of Monday, taking into account the latest updates, there had been 1,005,504 "irregular arrivals" into Europe in 2015.

The figures show that the vast majority -- 971,289 -- have come by sea over the Mediterranean. Another 34,215 have crossed from Turkey into Bulgaria and Greece by land.

Among those traveling by sea, 3,695 are known to have drowned or remain missing as they attempted to cross the sea on unseaworthy boats, according to IOM figures. That's a rate of more than 10 deaths each day this year.

One in every two of those crossing the Mediterranean this year -- half a million people -- were Syrians escaping the grinding, four-year civil war in their homeland.

More than 4 million Syrians have fled the conflict, creating the worst refugee crisis seen in 25 years, according to the United Nations.

Afghans accounted for 20% of the migrant flow, and Iraqis 7%.

A 'manageable' crisis

The startling human tide has presented European leaders, already grappling with the Eurozone debt crisis, with a fresh challenge -- one that has created political rifts and thrown the European goal of border-free travel into question.

IOM Director General William Lacy Swing said the numbers were significant, but not unmanageable.

"The numbers are important, but there's also a recognition that they're going into a population area of 550 million," he told CNN.

"If there were not a crisis of solidarity and leadership within the European Union, whereby others would follow the very important, courageous and visionary leadership of (German) Chancellor (Angela) Merkel and open their doors, then dispersed among 28 countries, it would have been much more manageable."

Germany, the most economically powerful country in the European Union, has led the way in extending a welcome to migrants, becoming the destination of choice for many entering Europe.

The country is set to take in more than a million asylum seekers this year, considerably more than any other country in the European Union , and has set aside more than $6 billion to help feed and house the new arrivals.

But where Merkel has opened doors, other European leaders have put up fences.

Unequal burden

Swing contrasted Europe's migrant burden with that of Syria's neighbors, who were accommodating most of the 4 million refugees from the conflict.

"Turkey is now the largest refugee-hosting country in the world, with close to 2.5 million," he said.

"Lebanon, with a population of less than 5 million, is hosting more than a million, and water-poor Jordan is giving 10 million liters of water every day to the million in their refugee camps."

"You cannot have unbroken simultaneous conflict from the western bulge of Africa to the Himalayas without expecting that a lot of people will be heading north, and obviously the resolution of the Syrian conflict is key to everything here," he said.

Deadliest route

The numbers of migrants into Europe have exploded in 2015 as an unprecedented surge of people have fled wars, persecution and poverty in the Middle East and Africa.

More than 970,000 migrants have entered Europe by crossing the Mediterranean so far this year, dwarfing the 219,000 who made the same crossing in 2014, according to the United Nations

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More people -- 221,000 -- crossed the Mediterranean in October of 2015, the busiest month for migration into Europe, than in the whole of 2014.

The Mediterranean, where nearly 3,700 people died this year, has become "the deadliest route for migrants on our planet," Swing has said.

At least 11 more, including three children, died Tuesday when their boat capsized while making the perilous journey from Turkey to Greece, Turkey's semiofficial Anadolu Agency reported.

By contrast, there have been 6,029 deaths between 1998 and 2013 along the second-deadliest border: the one between the United States and Mexico, the International Organization for Migration said.

Deaths are also commonplace along land routes into Europe. In August, Austrian authorities found the bodies of 71 migrants , believed to be from Syria , who had suffocated in a truck abandoned along a highway.

More than 80% through Greece

The overwhelming majority of migrants -- 821,008, or 81.6% -- arrived in Europe in Greece, the IOM said. The second-highest number of arrivals -- 150,317 -- were in Italy, with the remainder in Bulgaria, Spain, Cyprus and Malta, in that order.

According to an IOM statement released this month, the top five nationalities arriving in Greece were from Syria, Afghanistan, Iraq, Pakistan and Albania.

The top five nationalities arriving in Italy were Eritrean, Nigerian, Somalian, Sudanese and Syrian, the IOM said, citing figures from the Italian Interior Ministry.

Eritreans are running from a life of repression and abject poverty, fleeing "one of the poorest countries in the world and a closed and highly securitized state under an authoritarian government," according to a report by the Regional Mixed Migration Secretariat in Nairobi last year

Photos: 24 hours of Europe's migration crisis Migrants wear identification bracelets aboard a Norwegian ship during a search-and-rescue mission off the Libyan coast on Tuesday, September 1. Europe is in the midst of a migration crisis. Desperate men and women, often with children in tow, are fleeing wars and poverty to find a better life on the continent. But their voyages, both on land and on sea, can be dangerous and sometimes deadly. Hide Caption 1 of 13 Photos: 24 hours of Europe's migration crisis Hide Caption 2 of 13 Photos: 24 hours of Europe's migration crisis The body of a drowned migrant remains on a shore in Zuwara, Libya. In the last week , two boats carrying hundreds of people capsized near Zuwara, killing at least 84, officials said. Hide Caption 3 of 13 Photos: 24 hours of Europe's migration crisis A migrant shouts at Macedonian police officers while trying to cross Greece's northern border into Macedonia. About 1,500 migrants were waiting to cross the border. Hide Caption 4 of 13 Photos: 24 hours of Europe's migration crisis A young girl from Iraq waits for registration with her family outside the main station in Munich, Germany. Hundreds of migrants are arriving every day. Hide Caption 5 of 13 Photos: 24 hours of Europe's migration crisis Migrants sit outside the main station in Munich as they wait for their chance to register. Hide Caption 6 of 13 Photos: 24 hours of Europe's migration crisis A group of refugees continues its journey through Hungary after crossing the Serbian border. Hide Caption 7 of 13 Photos: 24 hours of Europe's migration crisis Syrian refugees walk across railways tracks next to the Serbian town of Horgos to cross the border and enter Hungary. Hide Caption 8 of 13 Photos: 24 hours of Europe's migration crisis Migrants sit in a police bus in Pocking, Germany, after making their way to the country from Austria. Hide Caption 9 of 13 Photos: 24 hours of Europe's migration crisis Migrants from Afghanistan drink tea at a Paris school where they found shelter. Hide Caption 10 of 13 Photos: 24 hours of Europe's migration crisis A migrant sleeps on a sidewalk in Berlin near the reception center for refugees and asylum seekers. Hide Caption 11 of 13 Photos: 24 hours of Europe's migration crisis Migrants walk on a rocky beach in Ventimiglia, Italy, where they set up camp near the French border. Hide Caption 12 of 13 Photos: 24 hours of Europe's migration crisis Refugee children sleep near a railway station in Budapest, Hungary. Hide Caption 13 of 13

European response

European leaders have hashed out a plan to resettle 160,000 refugees. But a massive gap remains between what they have pledged to do and what remains to be done.

And public sentiment toward the migrants remains mixed across the continent.

A photograph of a drowned 3-year-old Syrian Kurdish boy on a Turkish beach triggered an international wave of public sympathy for migrants.

But subsequent events, such as the revelation that one of the Paris attackers entered Europe alongside Syrian migrants landing in Greece, have helped cool goodwill and have boosted the fortunes of far-right political movements.

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U.N. High Commissioner for Refugees António Guterres said that in the face of rising anti-migrant sentiment, it was "important to recognize the positive contributions that refugees and migrants make to the societies in which they live and also honor core European values: protecting lives, upholding human rights and promoting tolerance and diversity."

Swing, meanwhile, accused the West of having "refugee amnesia."

"We must remember that our organization and the U.N. High Commission for Refugees were created in 1951 precisely to take Europeans ravaged by the Second World War to safe shores in Canada, the U.S., Australia and elsewhere," he said.

"If we are creative in using our visa policies to give temporary protective status to everyone so there is a measure of support there ... then I think it is a manageable proposition," he said.

The number of people coming from North Africa across the Mediterranean into Italy dropped slightly this year, from 170,000 in 2014 to around 150,000.