WASHINGTON — Undocumented immigrants who crossed into the United States after July 16 are supposed to be subject to the Trump administration's toughest asylum policy yet: If they did not first seek asylum in a country they passed through on their way to the U.S., and qualify for no other protections, they are to be fast-tracked for deportation.

But Immigration and Customs Enforcement told NBC News they have had zero deportations of immigrants under the new policy.

"Returns under the IFR policy have not started," ICE spokeswoman Paige Hughes said, referring to the "interim final rule" the Trump administration announced this summer.

Instead, immigration attorneys say, immigrants who have been ordered deported under the new policy are languishing in detention inside the U.S. because they have no right to stay but also have not been put on flights back to their home country.

It is not clear why ICE has not yet started deporting immigrants subject to the new policy. One former official said there is some confusion inside the agency about whether the immigrants should be deported back to their country of origin or the countries where they could have first claimed asylum.

Lee Gelernt, deputy director of the American Civil Liberties Union's Immigrants' Rights Project, said his group is representing immigrants subject to the rule.

"We have plaintiffs who have received final orders of removal based on the rule and are currently in detention," Gelernt said, adding that some have been detained for more than a month.

The Department of Homeland Security did not respond to a request for comment on why immigrants are being denied asylum under the policy but not deported.

Immigrants who are denied asylum under the policy can apply to stay in the U.S. under what is known as "withholding of removal" or the Convention Against Torture, both of which present higher bars for migrants to meet. But even those who have been denied those protections and given final orders of removal continue to languish in ICE detention centers.

Keeping asylum-seekers with deportation orders in ICE detention could fill the capacity and drain the resources at a time when the administration is seeking to detain more undocumented immigrants and release fewer into the U.S.

There has been much confusion over the policy since the administration said it would become effective immediately in the surprise announcement in July. Many questioned how the policy could be legally applied when countries such as El Salvador and Guatemala were not considered "safe third countries" for asylum-seekers, as defined in international law, or when Mexico had not agreed to such a deal.

The rule was first enjoined by courts, but the injunction was lifted by the Supreme Court on Sept. 11. At that point, U.S. Citizenship and Immigration Services, the agency within DHS responsible for asylum screening, said anyone who had entered the country since July 16, when the rule was first issued, would be subject to the rule.

A spokesman for the agency said that since the Supreme Court decision, "USCIS has fully implemented the IFR on a nationwide basis," again referring to the interim final rule.

But even top DHS officials seem to have some confusion over the policy's implementation. Speaking at the White House last week, acting Customs and Border Protection Commissioner Mark Morgan said, "I'm here to tell you today, we are instituting that asylum IFR this week."

Two CBP officials later told NBC News that Morgan misspoke.