SAN DIEGO (AP) — Immigrant advocacy groups said Tuesday that U.S. Customs and Border Protection officers are allegedly turning away asylum-seekers before their claims can be heard, violating obligations under U.S. and international law.

The groups said they began fielding reports in the summer that border crossers entering the country from Mexico were being told that they couldn't seek asylum, that they needed visas, or that that they first had to petition Mexican authorities for relief. Under U.S. law, any foreigner may claim asylum.

Many are left with the impression that the U.S. is no longer considering asylum requests, according to the complaint filed Friday to the U.S. Department of Homeland Security's inspector general. Six groups, including the American Immigration Lawyers Association, American Civil Liberties Union and American Immigration Council, urged an investigation "to fully address this alarming new trend."

Requests for asylum and other forms of humanitarian relief have surged in recent years, with many crossers turning themselves in instead of trying to avoid capture. After clearing a "credible fear" interview, their cases move to immigration courts, a process that could take years and allow them to remain in the country until a decision is reached.

U.S. Citizenship and Immigration Services, which does the initial screening, said it had 92,071 cases in the 2016 fiscal year, nearly double the 47,928 cases it handled the previous year and more than 16 times the 5,523 cases in 2009.

The complaint highlights several cases at border crossings from California to Texas. A Salvadoran woman who said she was receiving death threats at home over her membership in a political party was allegedly laughed at, threatened and turned away with her 3-year-old son when she sought protection at a south Texas crossing in November. A former Mexican police officer who had been "brutally attacked by a cartel" was allegedly told by officers in San Diego in July that asylum applications were not being accepted, forcing him into hiding.

Customs and Border Protection, which is part of the Homeland Security Department, said in a statement that there has been no policy change on asylum procedures and that it doesn't tolerate any abuse. If someone expresses fear of being returned to their home country, the person must be sent to an asylum officer for the initial screening.

"The United States has long adhered to international laws and conventions allowing people to seek asylum on grounds that they are being persecuted because of their race, religion, nationality, political beliefs or other factors," the agency said.