More than 2,000 illegal immigrants were turned loose on American streets after serving prison sentences last year - often because their home countries refused to take them back - and many subsequently committed crimes including rape and murder, a key lawmaker charged Monday.

The claim, by Sen. Charles Grassley, R-Iowa, comes a week after a federal audit blamed the Department of Homeland Security and an uncooperative Haiti for an illegal immigrant being freed to kill a Connecticut woman.

Grassley, who chairs the Senate Judiciary Committee, called on the Obama administration to put renewed pressure on countries that won’t take back their own criminals after they have been ticketed for deportation.

“Dangerous criminals, including murderers, are being released every day because their home countries will not cooperate in taking them back,” Grassley wrote in a June 27 letter to Homeland Security Secretary Jeh Johnson.

“Many times, these individuals have criminal histories in addition to entering the country illegally or overstaying their visa.”

Illegal immigrants convicted of crimes typically must serve all or part of their prison sentences in the U.S., and then are sent home under diplomatic agreements between the U.S. and other countries.

In 2015, said Grassley, some 2,166 individuals were released in the United States and not deported either because their countries would not readmit them or the U.S. government did not even try. In the two preceding years, more than 6,100 inmates slated for deportation were released within the U.S., Grassley said.

Some 23 countries are labeled as uncooperative, with the five worst being Cuba, China, Somalia, India, and Ghana, and U.S. Immigrations and Customs Enforcement is monitoring another 62 nations where cooperation is strained, Grassley said.

“This is a serious problem that has been festering for years, but is getting worse as countries realize that they can get away with just refusing to accept back their citizens who are criminals,” said Jessica Vaughan, director of Policy Studies for the Washington-based Center for Immigration Studies.

“What is equally frustrating is that the Obama administration has continuously refused to use the tools that Congress has provided and the leverage that we have with many of the recalcitrant countries, even as the roster of victims from these criminal aliens grows longer every month.”

There are a number of horrific cases involving victims of criminal aliens, Vaughan noted, including one highlighted by The Department of Homeland Security’s Inspector General last week. That report examined the circumstances that led to the murder of 25-year-old Casey Chadwick by Haitian national Jean Jacques, and found the agency’s overwhelmed Immigration and Customs Enforcement bureau should have booted Jacques from the U.S. prior to the killing.

In Jacques’ case, Haiti denied his entry three times when Immigration and Customs Enforcement tried to deport him, claiming there was no proof he was a Haitian citizen.

Haiti refused to allow U.S. officials to obtain his birth certificate, and a 2001 U.S. Supreme Court decision limits how long immigration officials can detain people without deporting them. Jacques, who was held for a total of 205 days, was released.

A second high-profile case highlighted by both Grassley and House Judiciary Committee Chairman Bob Goodlatte, R-Va., demonstrates the Obama administration’s failure to deport criminal illegal immigrants to cooperative nations. It occurred June 13, when Johnny Josue Sanchez allegedly murdered five people in Los Angeles by intentionally setting fire to the building where they were sleeping.

Border Patrol agents had apprehended Sanchez, a Honduras citizen in the U.S. illegally, in November 2012, and transferred him to the custody of ICE, but he was released a week later after ICE noted Sanchez did not have a criminal history or previous immigration violation.

Since entering the country, Sanchez has been arrested on multiple charges, including in January 2016 for domestic violence, and again in May and June 2016 just days before the murders, but ICE did not detain him or place him in removal proceedings, Grassley and Goodlatte said. Sanchez has been charged with five counts of murder and could be sentenced to the death penalty.

Asked for comment by FoxNews.com, ICE Western Regional Communications Director/Spokesperson Virginia Kice said, ”Following his arrest by local authorities earlier this week, ICE conducted a follow-up review of Mr. Sanchez’s case. The review showed that, for unknown reasons, Mr. Sanchez was never placed in immigration proceedings, although the others arrested with him were. ICE’s inquiry into to matter is continuing.”

“These are preventable, needless crimes that American communities should not have to put up with,” Vaughan said.

One of the worst offending countries is Cuba. More than 35,000 Cubans, including 28,000 who are convicted criminals, have been ordered deported but remain on U.S. soil, a higher number of non-departed criminals than any other country except for Mexico, according to Vaughan.

She suggested that DHA could work with the State Department, which could withhold visas for offending countries until they cooperated.

Keeping illegal immigrants who have already committed violent crimes puts Americans at unnecessary risk, said Claude Arnold, retired special agent in charge for ICE's Los Angeles bureau of Homeland Security Investigations, who also was a deportation officer handling a high volume of criminal alien cases involving countries that did not want to take back their citizens.

“We have enough problems with our own criminals. We should not have to hold on to criminals from other countries indefinitely,” Arnold said.

Grassley said Congress addressed this problem when it amended the Immigration and Nationality Act to require the Secretary of State to discontinue granting visas to a country upon receiving notice from the Department of Homeland Security that the country has denied or is unreasonably delaying accepting a citizen, subject, national or resident of that country.

“This tool has been used only once, in the case of Guyana in 2001, where it had an immediate effect, resulting in obtaining cooperation from Guyana within two months,” Grassley said.

Grassley told Johnson he wants answers as to why the DHS is not using the sanctions authority to get full cooperation, saying he is frustrated with the “inadequacy” of the Department of Homeland Security’s efforts to persuade recalcitrant countries to cooperate.

“Lives are being lost, the public’s safety is at risk, and American families are suffering,” Grassley said. “It cannot continue.”

“Although the majority of the countries in the world adhere to their international obligation to accept the timely return of their citizens, ICE has confronted unique challenges with those countries that systematically refuse or delay the repatriation of their nationals,” ICE spokesperson Jennifer Elzea told FoxNews.com.

“Despite ICE’s continued efforts, a number of factors constrain ICE’s ability to improve the level of repatriations to those nations. Such factors include: limited diplomatic relations with some countries; the countries’ own internal bureaucratic processes, which foreign governments at times rely upon in order to delay the repatriation process; and foreign governments that simply do not view repatriation as a priority.”