The incidents came during the same year the camp suffered a rash of suicide attempts after Major-General Geoffrey Miller took command of the prison with a mandate to get more information from prisoners accused of links to al-Qaida or the ousted Afghan Taliban government.
Between 18 August and 26 August, 23 detainees tried to hang or strangle themselves with pieces of clothing and other items in their cells, demonstrating "self-injurious behaviour", the US Southern Command in Miami said in a statement on Monday.
Ten detainees made a mass suicide attempt on 22 August alone.
US Southern Command described it as "a coordinated effort to disrupt camp operations and challenge a new group of security guards from the just-completed unit rotation".
Guantanamo officials classified two of the incidents as attempted suicides and informed reporters.
But they did not previously release information about the mass hangings and stranglings during that period.
US officials say the number of
'self-harm' incidents are down
Those incidents were mentioned casually during a visit earlier this month by three journalists, but officials then immediately denied there had been a mass suicide attempt.
Further attempts to get details brought a statement on Friday night, with some clarifications provided on Monday by military officials at Guantanamo Bay and the US Southern Command.
Alistair Hodgett, a spokesman for Amnesty International's office in Washington, was critical of the delay in reporting the incident.
Interrogation methods blamed
"When you have suicide attempts or so-called self-harm incidents, it shows the type of impact indefinite detention can have, but it also points to the extreme measures the Pentagon is taking to cover up things that have happened in Guantanamo," Hodgett said.
"What we've seen is that it wasn't simply a rotation of forces but an attempt to toughen up the interrogation techniques and processes."
Officials said they differentiated between a suicide attempt in which a detainee could have died without intervention and a "gesture" they considered aimed only at getting attention.
Army General Jay Hood, who succeeded Miller as the detention mission's commander last year, has said the number of incidents has decreased since 2003, when the military set up a psychiatric ward.
Incidents played down
In 2003, there were 350 "self-harm" incidents, including 120 "hanging gestures", according to Lieutenant-Colonel Leon Sumpter, a spokesman for the detention mission.
Last year, there were 110 self-harm incidents, he said.
"When you have suicide attempts or so-called self-harm incidents, it points to the extreme measures the Pentagon is taking to cover up things in Guantanamo"
"The Joint Detention Operations Group continually assesses the camp's population for whom the informal leaders are, the mood of the detainees, and their ability to communicate with each other," Southern Command said in a statement.
"That assessment has enabled the leadership to take numerous measures to reduce the opportunity for detainees to communicate a coordinated self-harm incident, or strike out at another detainee or the guard force."
The military has reported 34 suicide attempts since the camp opened in 2002, including one prisoner going into a coma and sustaining memory loss from brain damage.
Of the 23 men who tried to hang or strangle themselves during the 2003 protest, two required hospital treatment and then were transferred to the psychiatric ward, the military statement said.
Sixteen remain at Guantanamo Bay, while seven were transferred to other countries, the statement said without giving details. Some transferred detainees have been released while others continue to be detained in their native or other countries.