The Department of Homeland Security is asking the State Department to sanction four countries that have consistently refused to readmit people facing deportation from the U.S.

The request, made by acting Secretary Elaine Duke in a letter last week, comes after immigration authorities have been forced to release people who are in the U.S. illegally because their home countries declined to issue the necessary travel documents for their return, DHS spokesman David Lapan said at a press briefing Wednesday.

"You may have individuals from foreign countries that have committed crimes in the United States and been convicted – in some cases have served sentences – and when they’re released from prison they remain in the United States because their countries won’t take them back," Lapan said.

He later allowed that there were also many immigrants released under such circumstances who had not committed any crimes and who were detained on civil immigration violations.

Lapan would not identify which nations are facing sanctions, but they are among a list of 12 so-called "recalcitrant countries" identified by DHS: Burma, Cambodia, China, Cuba, Eritrea, Guinea, Hong Kong, Iran, Laos, Morocco, South Sudan and Vietnam.

The letter from DHS could effectively suspend travel to the U.S. from the four designated countries. Section 243(d) of the Immigration and Nationality Act requires the State Department to stop granting travel visas in recalcitrant countries when it such a request to do so from the Homeland Security secretary.

The State Department on Wednesday confirmed that it had received the letter from DHS last week, but it declined to say whether particular sets of officials or individuals would be affected by a visa suspension.

"We follow a standard process to implement a visa suspension as expeditiously as possible in the manner the Secretary determines most appropriate under the circumstances to achieve the desired goal," the agency said in a statement. "That process includes internal discussions with, and official notification to, affected countries. We are not going to get ahead of that process."

According to 243(d), the suspension could affect "citizens, subjects, nationals, and residents of that country." A State Department official confirmed that a suspension "may include any category of visa applicant, as determined by the Department on a country-by-country basis."

Such punishments, however, have been rare in recent years and narrow in scope. Presidents George W. Bush and Barack Obama sanctioned Guyana and Gambia in 2001 and 2016, respectively, but limited the impact to the countries' government officials.

DHS's letter last week to the State Department comes as the Trump administration has made a priority of deporting people in the country illegally. The president, on the campaign trail last summer, laced into "countries that refuse to take their people back after they’ve been ordered to leave the United States."

"Not going to happen with me, not going to happen with me," Trump said at a speech in Phoenix in August 2016.

Countries can get removed from the list if they cooperate with U.S. efforts. Iraq, for example, was on a list of some 22 countries considered recalcitrant, but it was removed after high-level government negotiations led to an agreement to again begin accepting deported nationals, Lapan said.

"Countries can take steps to be removed from the list," the spokesman said. "Our goal is to get countries to agree to accept the return of their nationals."