Washington ? Suspected or convicted foreign-born terrorists have exploited federal immigration laws over the last decade to enter or remain in the United States illegally, according to a report set for release today.

Once in the country, some of them became naturalized citizens, says the report distributed by the Center for Immigration Studies, an advocate for stricter immigration policies.

The report provides newly compiled data on U.S. terror arrests to illustrate gaps in the nation’s border security, visa approval and immigration systems. It was written by Janice Kephart, who served as counsel to the 9-11 Commission that investigated missteps leading to the Sept. 11, 2001, attacks.

“The attack of 9-11 was not an isolated instance of al-Qaida infiltration into the United States,” the 46-page report found.

Overall, 59 of 94 foreign-born nationals who were either convicted or indicted on terror charges broke federal immigration laws to enter or remain in the country between 1993 and 2004, the report found.

The report identified many of the immigrants as affiliated with at least one terror organization, including 40 with al-Qaida, 16 with Hamas, 16 with the Palestinian or Egyptian Islamic Jihad, and six with Hezbollah.

Tightening U.S. borders has become a top priority for Homeland Security Secretary Michael Chertoff, who last week called immigration enforcement an issue of utmost importance. The department has enacted a slew of programs – including stricter background checks, visa security systems and sharing intelligence with international allies – to harden immigration laws against terrorists, said spokesman Russ Knocke.

Recent studies indicate immigration-related cases made up nearly 33 percent of all federal prosecutions last year – more than any other crime.