WASHINGTON/MEXICO CITY (Reuters) - The United States will soon send non-Mexican migrants who cross the U.S. southern border back to wait in Mexico while their U.S. asylum requests are processed, a major change in immigration policy, the Trump administration announced on Thursday.

Immigrant advocates and human rights experts quickly denounced the policy change as illegal and violating the rights of refugees.

Mexico’s government said that it would accept some of those migrants for humanitarian reasons, in what many will see as an early concession to U.S. President Donald Trump’s administration by Mexico’s new president, Andres Manuel Lopez Obrador, who took office on Dec. 1.

“We want to discourage those who are claiming asylum fraudulently,” U.S. Homeland Security Secretary Kirstjen Nielsen told a congressional committee on Thursday, describing the plan.

In response to the plan, Mexico’s foreign ministry underscored that it still has the right to admit or reject the entry of foreigners into its territory.

“Mexico’s government has decided to take the following actions to benefit migrants, in particular unaccompanied and accompanied minors, and to protect the rights of those who want to start an asylum process in the United States,” the foreign ministry said.

But there appeared to be initial confusion within the Mexican government about the plan. Tonatiuh Guillén, who as head of Mexico’s National Migration Institute regulates migration in the country, said at a news conference on Thursday that the country would not be able to receive migrants from other countries until the regulatory framework had been established.

“We can’t begin to operate, we can’t begin to receive. We are not in a place to receive,” he said. “When will we able to do it? When the regulatory issues and operational issues are resolved,” he said.

Department of Homeland Security officials told reporters on condition of anonymity that the Mexican government has said asylum seekers would have access to attorneys in Mexico and that migrants would be able to enter the United States for their court hearings, without giving more details about how the process would work.

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“Operationally this will look a little bit different at different ports of entry simply based on what the infrastructure is like in the area,” said one official. “We are not implementing this on the entire U.S. border all at once.”

Nielsen said the new policy will not apply to Central American unaccompanied children, who have some special protections under U.S. law.

The administration is invoking a section of the Immigration and Nationality Act allowing the government to return migrants to a foreign country bordering the United States pending their immigration proceedings.

“We remain convinced that this is a power that the president was granted by Congress to execute exactly the way we have,” U.S. Secretary of State Mike Pompeo said in an interview with Fox News show host Laura Ingraham. “We’ve had lots of thought and legal review of this. We are confident that we are on firm ground.”

But the section of law being used by the Trump administration exempts anyone who is found inadmissible at the border because of a lack of documents, rather than for a criminal conviction, said Stephen Legomsky, a professor at the Washington University School of Law in St. Louis and a former senior DHS official during the Obama administration.

“That means the exemption to that section would apply to virtually every asylum seeker at the border,” he said.

‘NOT A SAFE COUNTRY’

Serious doubts remain over whether Mexico can keep vulnerable asylum seekers safe. Authorities are investigating the deaths of two Honduran teenagers kidnapped and killed in the border city of Tijuana last weekend.

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Immigrant and human rights advocates swiftly denounced the new policy, saying it violated international law and would put migrants at further risk.

“Make no mistake — Mexico is not a safe country for all people seeking protection,” said Amnesty International Executive Director Margaret Huang. “Many people seeking asylum in the United States face discrimination, exploitation, sexual assault, murder, or the possibility of being disappeared while traveling through Mexico or while forced to wait for extraordinarily long times in Mexican border towns.”

Trump tweeted on Nov. 24 that migrants at the U.S.-Mexico border would stay in Mexico until their asylum claims were individually approved in U.S. courts.

But Kennji Kizuka of the nonprofit group Human Rights First said serious questions remain about implementation of the plan.

“The administration seems to have no plan,” Kizuka said in a statement. “Will lawyers be able to visit their clients before hearings? Where will those hearings take place? We know that access to counsel is one of the most important factors in whether or not an asylum seeker is able to live in safety in the United States.”

The arrival of several thousand Central Americans in Tijuana about a month ago prompted Trump to mobilize the U.S. military to beef up border security. At the same time, the Trump administration has restricted the number of asylum applications accepted per day, saying they do not have the capacity to process more.

Illegal crossings at the southern border have dropped dramatically since the late 1970s, but in recent years applications for asylum have ballooned and more Central American families and unaccompanied children are migrating to the United States.