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WASHINGTON — After several years that saw more undocumented immigrants leaving the USA than entering, illegal immigration may be back on the rise, according to a report released Monday.

The total number of undocumented immigrants reached 11.7 million in 2012, representing a slow increase that is nearing the country's all-time high of 12.2 million undocumented immigrants in 2009, according to the report from the Pew Hispanic Center, a research group.

The new figures come as Congress is trying to pass a comprehensive overhaul of the nation's immigration laws designed to stop future waves of undocumented immigrants in the country.

The Senate passed a bill in July that would dedicate $46 billion to securing America's southern border with Mexico and allow most of those 11.7 million undocumented immigrants to apply for U.S. citizenship after 13 years. Republicans in the House of Representatives reluctant to grant citizenship to undocumented immigrants before fully securing the border are sure to use the new data to bolster their case.

Tamar Jacoby, president of ImmigrationWorks USA, a business lobby that supported the Senate immigration bill, said there were three main reasons that undocumented immigration fell so dramatically during a stretch from 2007 to 2009. The U.S. economy was shrinking, border enforcement continued getting tougher and the Mexican economy was improving to the point that many would-be immigrants stayed home.

"Two of those things have not changed," Jacoby said. "Border enforcement is still very tough. And the situation in Mexico has not turned south. So the only conclusion I can come up with is the U.S. economy is improving and attracting more workers."

Others put the blame for the increase in illegal immigration squarely on President Obama's unwillingness to fully enforce immigration laws, both at the border and inside the country.

Rosemary Jenks, director of government relations for NumbersUSA, a group that opposed the Senate bill, said Obama's Department of Homeland Security has methodically cut back on worksite raids targeting undocumented workers and scaled back deportations of people identified as being in the country illegally. That has left "absolutely no disincentive" for people in other countries thinking about trying to enter illegally.

"(The new numbers) mean we obviously do not have secure borders," Jenks said. "Once an illegal alien is in the United States, there is virtually no fear of being caught and removed. This administration has undermined immigration enforcement consistently, and that's having an impact."

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