WASHINGTON (AP) — The Trump administration spent at least $40 million to deport roughly 300 migrants to countries other than their own as immigration officials expanded the practice over the last year to carry out President Donald Trump's goals of quickly removing immigrants from the U.S., according to a report compiled by the Democratic staff of the Senate Foreign Relations Committee.

The Democrats on the Foreign Relations panel, led by Sen. Jeanne Shaheen, criticize the practice of third country deportations as “costly, wasteful and poorly monitored” in the report and call for “serious scrutiny of a policy that now operates largely in the dark.”

The State Department, which oversees the negotiations to implement the programs, has stood behind the practice of third country deportations and defended it as a part of Trump’s campaign to end illegal immigration.

“We've arrested people that are members of gangs and we've deported them. We don't want gang members in our country,” Secretary of State Marco Rubio responded when asked about some of the third country deportations at a Senate hearing last month.

The report, which is the first congressional review of the agreements, found lump sum payments ranging between $4.7 million and $7.5 million to five countries — Equatorial Guinea, Rwanda, El Salvador, Eswatini and Palau — to deport migrants to those nations. El Salvador has received about 250 Venezuelan nationals in March last year, while the other nations received far fewer deportees, ranging from 29 sent to Equatorial Guinea to none sent to Palau so far, according to the report.

The nations examined in the report are just a fraction of the Trump administration's overall work to deport migrants to third countries. According to internal administration documents reviewed by The Associated Press, there are 47 third-country agreements at various stages of negotiation. Of those, 15 have been concluded and 10 are at or near conclusion.

The administration is also negotiating agreements with countries that will accept U.S. asylum seekers while their asylum claims are processed, according to the internal documents. There are 17 that are at various stages of negotiation, including 9 that have formally taken effect, although the administration claims that the agreements do not necessarily need to be concluded for people to be sent there.

Immigration advocacy groups have criticized the “third country” policy as a reckless tactic that violates due process rights and can strand deportees in countries with long histories of human rights violations and corruption.

During a visit to South Sudan, Democratic committee staff found a gated house with armed guards where deportees were held, including migrants from Vietnam and Mexico.

The Democrats also largely take aim at how wasteful and ineffective the policy may be. It details several instances of migrants being deported to a third country, only for the U.S. to later pay for another flight to return the migrant to their home country.

“In many cases, migrants could have been returned directly to their countries of origin, avoiding unnecessary flights and additional costs,” said Shaheen in a statement also signed by Democratic Sens. Chris Coons, Tammy Duckworth, Tim Kaine, Jack Rosen and Chris Van Hollen.

It also remains unclear what benefits the countries may receive — or expect — in return for accepting third-country nationals.

After an agreement was in place last year, South Sudan sent a list of requests to Washington that included American support for the prosecution of an opposition leader and sanctions relief for a senior official accused of diverting over a billion dollars in public funds, according to diplomatic communications made public by the State Department in January.

Shaheen has also questioned a $7.5 million payment sent to Equatorial Guinea that came at the same time the Trump administration was developing ties with the country's vice president, Teodoro “Teddy” Nguema Obiang. He is notorious among world leaders accused of corruption for a lavish lifestyle that has attracted the attention of prosecutors in several countries.