Washington: The United States has seen a mysterious surge of asylum seekers from India entering America illegally through the southwestern desert state of Arizona bordering Mexico, according to a media report.

Hundreds, and perhaps thousands, of  Indians over the past year have asked for asylum claiming to fear they may be persecuted if returned to their country, the Arizona Republic published in Phoenix, said in an investigative report.

They arrive after paying as much as $35,000 to be smuggled halfway around the globe, flying from India to Central America and then embarking on an arduous and often dangerous 3,000-mile journey through several countries, including Mexico, to reach Arizona, it said.

Some have been caught crossing illegally by the Border Patrol. More often, they are simply turning themselves in at legal border crossings in Nogales, Arizona, asking for asylum based on claims of political persecution, the U.S. daily said.

On a nightly basis, as  many as two dozen Indians who have managed to establish so-called "credible fear" of persecution during hearings with U.S. immigration asylum officers are set free at a bus station near the Phoenix Sky Harbour International Airport, it said.

Before their release, they are given notices to appear in immigration court at a future date, when a judge will decide whether to grant asylum.

In addition to the many hundreds who have already been released, hundreds more remain in detention centres in Eloy and Florence waiting for credible-fear hearings, the Republic said.

It is unclear, however, whether those asking for asylum are legitimately fleeing persecution and whether they intend to show up for their asylum hearings, the daily said.

In fiscal year 2012, nearly 10 percent of Indian asylum seekers failed to show up for their final asylum hearings in U.S. immigration courts nationwide , the daily said citing the Department of Justice.

Homeland Security buses staffed by Immigration and Customs Enforcement officers, routinely bring recently released  immigrants, who are deemed low-flight risks and not a danger to the community, to the bus station so they can arrange travel to meet relatives in other parts of the U.S.

About half the migrants getting off the buses each night are Spanish speakers from Guatemala, Honduras, El Salvador and other Central and South American countries, the U.S .daily said. The other half is Indians.

The Republic cited a U.S. State Department spokesperson Nicole Thompson as saying she is unaware of any mass conflict in India that would be contributing to an increase in asylum seekers from India.

But India is a complicated country with a "great degree of variance internally as far as the standard of living and income", she was quoted as saying.

Department of Homeland Security officials cited by the Republic said they are investigating the surge in Indian migrants at the Arizona border.

"DHS has implemented a collaborative, coordinated response to Indian apprehensions along the Southwest border," U.S. Customs and Border Protection spokesman Victor Brabble was quoted as saying in a written statement.

That  includes working with the governments of other countries to "analyse potential threats" and "identity and dismantle human smuggling networks", Brabble said.

The Arizona Republic said DHS officials refused its repeated requests to provide statistics for the number of Indians who have asked for asylum in Arizona, the number of Indians who have been held in detention and the number who have been released after establishing credible fear.