The roughly 200 million migrants worldwide were an important force for the world economy, the UN-backed study by the Global Commission on International Migration, a 19-member independent panel, showed. In addition to the trillions they spent in their host countries, they sent remittances of around $150 billion home, three times the amount the world officially devotes to developmental aid. An additional $300 billion may be transferred informally, the report added.

"In the 21st century, one of our most important challenges is to find ways to manage migration for the benefit of all -- of sending countries, receiving countries, transit countries and migrants themselves," UN Secretary General Kofi Annan said at the launch of the report. "I agree with the commission that we are not rising to the challenge yet. But I am convinced we must do so," Reuters quoted Annan as saying.

After the United States and Russia, Germany had the third greatest number of migrants, 7.3 million, 4.2 percent of the world's migrants, in 2000. Along with Belgium and Switzerland, the country also ranked third in the amount of remittances migrants send home: $8 billion in 2001. The same year Germany spent $5.68 billion on developmental aid.

Combatting xenophobia

Although the commission criticized the manner in which states treat migrants, it gave few detailed examples. It did though point out that the economies of industrial countries would collapse without foreign nurses, computer engineers or farm workers.

"If information percolated throughout economies, people would stop moaning about migrants taking away work," Mamphela Ramphele, a South African member of the commission and former senior World Bank official, said.

Over the past 35 years, the number of migrants worldwide has grown from 72 million to 200 million, around 10 million of whom are refugees. From 1990 to 2000, international migration accounted for 56 percent of population growth in the developed world, compared with 3 percent in developing nations, the report noted. And the numbers continue to grow.

"The expansion in the scale and scope of migration seems certain to continue for the foreseeable future and may well accelerate, due to the growing developmental, demographic and democratic disparities that exist between different regions of the world," the report said. "Migration is driven by some powerful economic, social and political forces, and states must acknowledge its reality."

"The international community has failed to realize the full potential of international migration and has not risen to the many opportunities and challenges it represents," the report said. It called for a "comprehensive, coherent and global action framework" for UN member nations' migration policies.

Harsh approaches to illegal immigration

The study also estimated that 2.5 to 4 million people move to other countries illegally each year. Though the report recognized the right of states to set rules to deal with illegal immigration, the authors were critical. "A purely restrictive approach to irregular migration is neither desirable nor feasible and may jeopardize the rights of migrants and refugees," they said.

The report pressed for improved cooperation among governments trying to tackle illegal immigration, combined with efforts to ensure legal migrants are "effectively integrated" in the countries where they settle.

"The role of migrants in promoting economic growth, development and poverty reduction should be recognized and reinforced," the report added. "Migration must become an integral part of global development strategies."

The commission was created in 2003 by UN head Kofi Annan to study policies worldwide, spurred by Brazil, Morocco, the Philippines, Sweden and Switzerland. Its members include Sweden's former migration minister, Jan Karlsson.

The report was based on statistics from the UN, the World Bank and the International Monetary Fund.