WASHINGTON — The Biden administration said Monday it is making asylum restrictions at the southern border even tougher, as it’s increasingly eager to show voters uneasy over immigration that it is taking a hard stance on border security.

The new rules, which toughen restrictions announced in June, bar migrants from being granted asylum when U.S. officials deem that the southern border is overwhelmed.

Under the previous rules, the U.S. could restrict asylum access when the number of migrants trying to enter the country between the official border crossings hit 2,500 per day. The daily numbers had to average below 1,500 per day for a week in order for the restrictions to be lifted.

The version rolled out Monday says the daily numbers will have to be below 1,500 for nearly a month before the restrictions can be lifted. And the administration is now counting all children toward that number, whereas previously only migrant children from Mexico were counted.

These changes, which go into effect on Tuesday, will make it much more difficult to lift the restrictions and allow people entering the country between the official border crossings eventually to apply for asylum in the U.S.

But the restrictions implemented in June have never been lifted because the numbers of border encounters have never gotten low enough for long enough, raising the question of why the administration felt the need to make them even tougher now. The seven-day average has gotten down to about 1,800 migrant encounters per day, the Department of Homeland Security said.

A senior administration official said Monday that the longer timeline was necessary to make sure that drops in immigration are sustained and not due to a one-time event. The official spoke on condition of anonymity to brief reporters about the tighter restrictions before they were made public.

Immigration advocates had harshly criticized the restrictions announced in June, saying the administration was slashing away at vital protections for people fleeing persecution.

Many weighed in Monday, saying that by making the rules even tougher the administration was sending people back into danger and not living up to its humanitarian obligations.

The American Immigration Lawyers Association said the new rule is effectively an asylum ban and that the exceptions aren’t as substantive as the administration has made them out to be.

The UN refugee agency said it had “profound concern” about the changes and that blocking asylum access violates international refugee law and “the humanitarian principles to which the United States has long been a leader.”

Secretary of Homeland Security Alejandro Mayorkas pushed back on suggestions that the updated rules amounted to an asylum ban. He said there were exceptions built into the rule for people who qualify and pointed to other programs such as an online appointment app the U.S. has that allows people to come to the U.S. and seek asylum.

“We have not cut off our asylum system,” the secretary said.

The exceptions include victims of a severe form of trafficking, who would still be allowed to apply for asylum.