(CBS) The U.S. government is preparing to free some two dozen terrorist suspects from its high-security prison in Cuba, defense officials said Monday.

The release is expected in the next several days, two senior Defense Department officials said on condition of anonymity.

They denied that the release is the result of a complaint by Secretary of State Colin Powell, who has pressed the Pentagon to move faster in determining the fate of the prisoners at Guantanamo, some of whom have been held a year and a half without charges and without access to lawyers.

In what officials said was a "strongly worded" letter, Powell told Defense Secretary Donald H. Rumsfeld that eight allies had complained about the holding of their citizens. He said failure to handle the prisoners correctly was undermining efforts to win international cooperation in the war on terror.

Pentagon officials said Monday that the April 14 letter was not a factor in the upcoming release, which they said was in the planning process for four weeks.

One official said that some 20 to 30 prisoners will be released from the prison opened in January 2002 at the Naval base at Guantanamo Bay.

He said he did not know what countries they were from, nor whether they would include any of several juveniles held there. News that several boys between the ages of 13 and 16 were among prisoners drew criticism from human rights groups and a call for their immediate release.

Some 660 prisoners from 42 countries are held, many captured during the war against al Qaeda in Afghanistan. Officials have declined to identify them, their countries or any other details about them, including the exact number held.

On Sunday, Rumsfeld said that prisoners at Guantanamo Bay in Cuba must be questioned by several agencies before they can be released and he blamed this "very slow" process for their continued detention.

The defense secretary added that he, too, would like to see the process move more quickly.

But, Rumsfeld said, the prisoners' cases are being reviewed by agencies including the FBI, the Justice Department, the State Department, the Pentagon, the CIA and the Immigration and Naturalization Service.

Some are interested in prosecuting the detainees for crimes they may have committed, while others are interested in gathering intelligence information to prevent future attacks.

"So, it's a complicated process. It is very slow," Rumsfeld said.

He said Powell, as America's chief diplomat, was making the case on behalf of foreign governments that want to see these prisoners released from the U.S. naval base in Cuba.

"Colin's job is to represent those countries into this interagency process and see if there isn't some way we can speed that up," he said. "I would like to see it move faster."

Since the prison was opened in January 2002, only 22 people are known to have been released. They were all men, including one who was mentally ill and another reported to be in his 70s.

Human rights advocates have criticized the Bush administration's plan to hold prisoners indefinitely and without trial, charges or access to lawyers.

Last month, some groups called for the immediate release of juveniles when it was learned that several boys between ages 13 and 16 were being held at the naval base in Cuba.

The teenagers are held in a "communal setting" separate from adult detainees' individual cells, but all were "captured as active combatants against U.S. forces" and are considered enemy combatants, said Lt. Col. Barry Johnson, chief spokesman for the mission.

Johnson would say only that the teenagers are "very few." However an official at the camp who spoke on condition of anonymity Wednesday said there were three youths.

Johnson would not say how old the youngest prisoner is. He confirmed their presence Tuesday following a report by Australia's ABC television that youths were being held at the camp.

"That the U.S. sees nothing wrong with holding children at Guantanamo and interrogating them is a shocking indicator of how cavalier the Bush administration has become about respecting human rights," said Amnesty International spokesman Alistair Hodgett.

Human Rights Watch said the United States was exacerbating a contentious situation.

The detention of youths "reflects our broader concerns that the U.S. never properly determined the legal status of those held in the conflict," said James Ross, legal adviser for Human Rights Watch in New York.

Holding "captured children … obviously makes the problem worse."

Johnson said juveniles are being held because "they have potential to provide important information in the ongoing war on terrorism."

He said "their release is contingent on the determination that they are not a threat to the (U.S.) nation and have no further intelligence value."

Lawyers have blamed the indefinite detentions for increasing depression and suicide attempts at the camp, which received the first detainees in January 2002.

Johnson reported a repeat attempt at suicide Monday night by a detainee who was under close supervision in the acute care unit of a new mental health ward.

That brings the number of suicide attempts to 25 by 17 individuals, with 15 attempts made this year, according to the military.