MEXICO CITY/NEW YORK (Reuters) - The United States began sending Central American families seeking asylum back to Mexico this week, a Mexican immigration source said on Thursday, while U.S. human rights groups sued the Trump administration, saying the policy puts migrants in danger.

FILE PHOTO: Police escort a bus bound to Monterrey, transporting Mexican migrants deported from the United States, as it leaves a bus station in Reynosa, Mexico January 11, 2019. Picture taken January 11, 2019. REUTERS/Tomas Bravo

Five families with a total of 16 people, including children from El Salvador, Honduras and Guatemala, arrived in the Mexican border city of Tijuana on Wednesday, according to a person who works in migration for the Mexican government, who asked not to be named.

In late January, the United States began sending non-Mexican migrants who had crossed at the U.S. border with Mexico back to Mexico to wait as their asylum requests are processed, a program called Migrant Protection Protocols. But until this week, only individual adults had been sent back, not children in family groups.

Rights groups say the program endangers asylum seekers by forcing them to remain in regions of Mexico experiencing record levels of violence.

“Both the U.S. and Mexican governments know that the border area is unsafe for women and children,” Michelle Brané, director of the Migrant Rights and Justice program at the Women’s Refugee Commission (WRC), said in a statement on the decision to return the families to Mexico.

“The U.S. government knows full well that asylum-seeking families are no threat to this nation.”

Sixty-three people have returned to Mexico so far under the program, the government source said.

Two shelters in Tijuana said they had received the families. They asked not to be named to avoid revealing their location.

The American Civil Liberties Union and immigrant rights groups filed a lawsuit on behalf of 11 anonymous asylum seekers on Thursday. The groups asked a U.S. judge to revoke the policy and order the government to bring the migrants back to the United States while their cases are processed.

The 11 asylum seekers from Central America were returned to Mexico since Jan. 30 to wait out their immigration cases, and now fear for their lives, according to the complaint.

The plaintiffs include a lesbian who said she was raped because of her sexual orientation and was forced to flee Honduras after her partner’s family threatened to kill them.

The lawsuit alleges the policy endangers migrants and violates U.S. immigration and administrative law, as well as universal norms of international law.

A spokesman for the U.S. Department of Justice said the government would defend the policy in court.

“Congress has explicitly authorized the Department of Homeland Security to return aliens arriving from a contiguous foreign territory to that territory during that alien’s immigration court proceedings,” said Steven Stafford of the DOJ.

In another sign of the political tension over immigration, the White House on Thursday said U.S. President Donald Trump will declare a national emergency to try to obtain funds for his promised wall on the Mexican border when he signs a bill to avert another government shutdown.

Mexico’s National Migration Institute and the U.S. Department of Homeland Security did not immediately respond to requests for comment.