Thousands of immigrants from India, mostly Sikhs, have crossed into the United States illegally at the southern tip of Texas in the last year, complaining of political and religious persecution at home, a major American newspaper reported Sunday. The surge of people migrating from India, a country which claims to be world's largest democracy, is "backing up court dockets, filling detention centers and triggering investigations", The Los Angeles Times said. More than 1,600 Indians have been caught since the influx began here early last year, while an undetermined number, perhaps thousands, are believed to have sneaked through undetected, according to U.S. border authorities. Hundreds have been released on their own recognizance or after posting bond, the report said. They catch buses or go to local Indian-run motels before flying north for the final leg of their months-long journeys. The Indian migration in some ways mirrors the journeys of previous waves of immigrants from far-flung places, such as China and Brazil, who have illegally crossed the U.S. border here, the Times said. But the suddenness and still-undetermined cause of the Indian migration baffles many border authorities and judges. The trend has caught the attention of anti-terrorism officials because of the pipeline's efficiency in delivering to America's doorstep large numbers of people from a troubled region, it said. "Authorities interview the immigrants, most of whom arrive with no documents, to ensure that people from neighbouring Pakistan or Middle Eastern countries are not slipping through," the report pointed out. There is no evidence that terrorists are using the smuggling pipeline, FBI and Department of Homeland Security officials said. The influx shows signs of accelerating: About 650 Indians were arrested in southern Texas in the last three months of 2010 alone. Indians are now the largest group of immigrants other than Latin Americans being caught at the Southwest border. The migration is the "most significant" human-smuggling trend being tracked by U.S. authorities, said Kumar Kibble, deputy director of Immigration and Customs Enforcement, or ICE. In 2009, the Border Patrol arrested only 99 Indians along the entire Southwest border. "It's a dramatic increase," Kibble said. "We do want to monitor these pipelines and shut them down because it is a vulnerability. They could either knowingly or unknowingly smuggle people into the U.S. that pose a national security threat." Most of the immigrants are from the Punjab or Gujarat states, the Times said. They are largely Sikhs who say they face religious persecution, or members of the Bharatiya Janata Party who say they are targeted for beatings by members of the National Congress Party. Many Indians begin their journey by flying from Mumbai to Dubai, then to South American countries such as Ecuador or Venezuela, according to authorities and immigration attorneys. Guatemala has emerged as the key transit hub into Mexico, they said. The roundabout journeys are necessary because Mexico requires visas for Indians. They sneak across the dangerous Guatemala-Mexico border and take buses or private vehicles to the closest U.S.-Mexico border. Mexican organized crime groups are suspected of being involved either in running the operations or in charging groups tolls to pass through their territory. The Indians usually wade across the Rio Grande, and then are shuttled from stash houses to transportation rings that take them north. David Aguilar, deputy commissioner of Customs and Border Protection, an agency within the Department of Homeland Security, said he believed a high percentage were caught as soon as they crossed the river. "We very intensely interview, look at their backgrounds, check them against any watch list," Aguilar said, adding that although India is not considered a "special interest" source country for terrorists, the undocumented immigrants are scrutinized as if it were. The detainees eventually claim asylum. In January, immigration court calendars at the area's two main detention facilities were full of the common Indian surnames Singh and Patel, and attorneys and judges struggled to keep up. Some attorneys had failed to file the necessary forms; interpreters were not always available. Judge Keith Hunsucker said more immigration judges would soon be assigned to handle the increased workload. Many detained immigrants clear the first hurdle toward a full asylum hearing by convincing asylum officers they have a "credible fear" of persecution if they return to India. They can then post a bond and move anywhere in the United States as long as they agree to appear for their next court date. Not all show up, however. "That's why I won't take their cases anymore," said Cathy Potter, a local immigration attorney who helped about 20 Indians get freed on bond last year. "It undermines my credibility. I don't want anything to do with this." The Times said the number of Indians have been granted asylum or deported was not known. Judges and attorneys are toughening up, however. Bond amounts have risen sharply in recent months, and attorneys say asylum claims are increasingly being rejected. Hundreds of immigrants have persuaded asylum officers and judges to grant credible-fear findings, clearing the way for bond hearings, the report said. Hunsucker, an immigration judge at the Port Isabel Detention Center near Brownsville, set bond amounts ranging from $15,000 to $40,000 for 10 Indians one recent morning. Most said they had relatives or friends in the U.S. willing to sponsor them, though the judge raised concerns about some. In one case, a young man said his sponsor was his cousin, a woman. But the faxed identification document of the cousin showed a picture of a man with a beard. The bond was set at $15,000.