Following the Supreme Court's decision to allow the Trump administration to go forward with its toughest asylum policy to date, officials from the Department of Justice and Homeland Security on Friday detailed how they would begin enforcement, including by turning back children who arrive at the southern border without their parents.

The new policy would make asylum seekers ineligible if they passed through another country on their way to the United States and did not first seek asylum there. The officials said they will return immigrants who arrived in the U.S. on or after July 16 to their home countries if they cannot prove they sought asylum elsewhere.

Immigration and human rights advocates have decried the policy, claiming it is in violation of the international right to claim asylum regardless of how one arrives in the country where they are seeking protection. Those arguments are still playing out in lower courts, which could ultimately end in the policy's reversal.

Even if asylum seekers are denied protection by another country, they are still eligible to apply in the United States, a DHS official said, if they can prove they tried to seek it elsewhere.

The officials said unaccompanied migrant children are awarded some additional protections, but will not be exempt from the rule.

Some exceptions do apply. For example, if an asylum seeker can prove to U.S. authorities that he or she has a fear of torture if returned home, they would be allowed to seek protection under the Convention Against Torture in the United States. Immigrants can also appeal their deportation decisions to an immigration judge.

The Trump administration has said the new policy is necessary to weed out asylum claims that are not likely to end in a favorable decision in court. Currently, the majority of initial claims for asylum are accepted but then ultimately denied by a judge. Due to a court backlog of over 400,000 asylum claims, many asylum seekers live in the United States for years before their court date or do not show up for their hearing.