A Honduran migrant prepares tortillas and rice at the Pan de Vida shelter for migrants where she and her two daughters are living while waiting their turn to apply for asylum in the U.S. in Ciudad Juarez, Mexico, Thursday, Sept. 12, 2019. Mexican Foreign Secretary Marcelo Ebrard said Thursday that Mexico's government doesn't agree with an

TIJUANA, Mexico (AP) — A new level of despair spread among tens of thousands of migrants waiting on the Mexican border to seek refuge in the U.S. as the Trump administration began enforcing radical new restrictions Thursday on who qualifies for asylum.

"The United States is the only option," Dunea Romero, a 31-year-old Honduran, lamented with tears in her eyes at a shelter in Tijuana. She said she packed a bag and fled her homeland with her two boys, ages 7 and 11, after learning that her abusive ex-husband, a powerful gang leader, was going to have her killed.

The new U.S. policy would effectively deny asylum to nearly all migrants arriving at the southern border who aren't from Mexico. It would disallow anyone who passes through another country without first seeking and failing to obtain asylum there.

The rule will fall most heavily on Central Americans, mainly Hondurans and Guatemalans, because they account for most people arrested or stopped at the border.

But it also represents an enormous setback for other asylum seekers, including large numbers of Africans, Haitians and Cubans who try to enter the United States by way of the Mexican border.

It is perhaps the biggest change to U.S. asylum policy since it was established in 1980 and the most consequential move of President Donald Trump's crackdown on immigration, a signature issue as he heads into a re-election campaign.

The Trump administration put the policy into effect the day after the Supreme Court cleared it to do so while legal challenges move forward.

Acting U.S. Customs and Border Protection Commissioner Mark Morgan called the high court's go-ahead a "big victory" in the administration's effort to curb the flow of migrants. Migrants and their advocates decried it as tantamount to a death sentence for many of those fleeing poverty and violence in their homelands.

Jessica Collins, a spokeswoman for U.S. Citizenship and Immigration Services, the agency that handles asylum cases, said it will be retroactive to July 16, when it was announced.

Collins said it will help remove one of the factors that impel people to set out for the United States, "leading to fewer individuals transiting through Mexico on a dangerous journey."

An unprecedented surge of asylum-seeking families from Central America has overwhelmed U.S. authorities during Trump's tenure, prompting the unprecedented response.

Under another Trump administration policy, introduced in January, more than 40,000 asylum seekers have been forced to wait in Mexico while their cases wind through the clogged American immigration courts.

In Tijuana on Thursday, Ngoh Elliot Takere of Cameroon stood only steps from the United States, frustrated after learning that he could be blocked from getting in. He has been waiting for two months in Mexico for his number to be called so he can submit a request for asylum.

The 28-year-old furniture maker said he left his war-torn African homeland after being jailed by police for being part of the English-speaking minority. He was released on the condition that he leave the country or be killed, he said. He said the military burned his family's home, killing his mother as she slept.

As for the possibility of being turned away by the United States, Takere said: "I can't think of that."

"In the U.S., I know I'll be protected," he said.

Many asylum seekers denied refuge under the new policy will be placed in fast-track deportation proceedings and flown to their home countries at U.S. expense, authorities said.

Some seeking refuge may get to stay in the United States through other legal avenues, including protection under the United Nations Convention Against Torture, but the threshold to qualify is much higher.

"Our Supreme Court is sentencing people to death. There are no safeguards, no institutions to stop this cruelty," the immigration-assistance group Al Otro Lado said in a statement. The Mexican government likewise called the high court's action "astonishing."

But Morgan said migrants with valid claims should instead be seeking asylum "from the first country they come in contact with."

"They shouldn't be paying the cartels thousands of dollars and risking their lives to take a 1,000-mile journey across several countries to get help," he said on Fox News.

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Attanasio reported from Ciudad Juarez, Mexico. Associated Press writers Mark Sherman and Colleen Long in Washington and Elliot Spagat in San Diego contributed to this report.

Photographed through a window screen, Central American migrants pass the time at the Pan de Vida shelter in Ciudad Juarez, Mexico, while waiting for their turn to request asylum in the United States, Thursday, Sept. 12, 2019. Mexican Foreign Secretary Marcelo Ebrard said Thursday that Mexico's government doesn't agree with an
Central American migrants clean the Pan de Vida shelter for migrants in Ciudad Juarez, Mexico, where they are staying while waiting for a chance to request asylum in the United States, Thursday, Sept. 12, 2019. Mexican Foreign Secretary Marcelo Ebrard said Thursday that Mexico's government doesn't agree with an
A migrant mother washes her son's face at the Pan de Vida shelter where they are living in Ciudad Juarez, Mexico, while waiting for a chance to request asylum in the United States, Thursday, Sept. 12, 2019. Mexican Foreign Secretary Marcelo Ebrard said Thursday that Mexico's government doesn't agree with an
Central American migrant kids pass the time at the Pan de Vida shelter in Ciudad Juarez, Mexico, while waiting with their families to request asylum in the United States, Thursday, Sept. 12, 2019. Mexican Foreign Secretary Marcelo Ebrard said Thursday that Mexico's government doesn't agree with an
Honduran migrant Dunea Romero, 31, helps helps make Honduran style nachos at the migrant shelter where she is living in Tijuana, Mexico, as she waits for her next asylum hearing in the U.S., Thursday, Sept. 12, 2019, on the border with San Diego. Romero, who was married to a powerful gang leader, grabbed passports for herself and two boys, ages 7 and 11, packed a bag and left the morning after a friend told her that her ex-husband had a hit out on her life. (AP Photo/Julie Watson)
Ngoh Elliot Takere gives an interview in Tijuana, Mexico, where he has been waiting for two months to apply for asylum in the U.S., Thursday, Sept. 12, 2019, on the border with San Diego. Takere left his war-torn Cameroon after being jailed by police for being part of the English speaking minority; paid $400 bail and was released on the condition that he leave the country or the French speaking government would track him down and kill him, he said. (AP Photo/Julie Watson)