Corruption plagues the agency that determines the legal status of immigrants, and its employees often don't conduct proper background checks of immigration applicants, a former agency official told lawmakers Thursday.

As a result, "the integrity of the United States immigration system has also been corrupted and the system is incapable of ensuring the security of our homeland," Michael Maxwell said.

"Ours is a system that rewards criminals, facilitates the movement of terrorists, (and) supports foreign agents," said Maxwell, who had been in charge of the Office of Security and Investigations at U.S. Citizenship and Immigration Services until resigning in February.

The agency's director, Emilio Gonzalez, has said that the Homeland Security Department's inspector general will investigate reports of fraud and sloppy procedures. Gonzalez also has insisted that security concerns come first even though the agency is under pressure to get through a backlog of immigration applications.

Angelica Alfonso-Royals, a spokeswoman, said Thursday the agency's top priority "continues to be preserving and enhancing the integrity of the immigration system." She said the agency has confidence in the system but continually strives for improvement and "it takes allegations seriously."

Maxwell testified before the House International Relations Committee's terrorism and nonproliferation panel. He alleged that the agency has awarded immigrant benefits, including citizenship, without complete background checks.

In addition, he said, the agency has failed to investigate more than 500 criminal complaints against its own employees for allegations that include bribery, harboring illegals, money laundering and aiding known terrorists or being influenced by foreign intelligence services.

In one example, Maxwell said, the agency employed an Iraqi-born U.S. citizen suspected of being a foreign intelligence agent to review asylum applications.

"These breaches compromise virtually every part of the immigration system itself, leaving vulnerabilities that have been and likely are being exploited by criminals and adversaries of the United States," Maxwell said.

He said the agency's senior officials repeatedly ignored major national security vulnerabilities, covered them up or dismissed them.