WASHINGTON - The American Civil Liberties Union (ACLU) wrote a letter to US Secretary of Defense Robert Gates Friday protesting the "inhumane and unlawful practice" of force-feeding hunger strikers at Guantanamo Bay prison.

File photo shows a detainee holding onto a fence as a US military guard walks within the grounds of the maximum security prison of Camp 5 at the Guantanamo Bay US Naval Base in Cuba. The American Civil Liberties Union (ACLU) wrote a letter to US Secretary of Defense Robert Gates Friday protesting the "inhumane and unlawful practice" of force-feeding hunger strikers at Guantanamo Bay prison. "I am writing to bring your attention to the cruel, inhuman, degrading and unlawful treatment of the thirty hunger striking detainees currently held at the Guantanamo Bay detention facility," wrote ACLU Human Rights Program director Jamil Dakwar.

Pentagon spokeswoman Cynthia Smith said there were 34 hunger strikers at the prison and that 25 of them were being force-fed. The ACLU said it based its estimates on media reports.

"Force-feeding is universally considered to be a form of cruel, inhuman and degrading treatment," Dakwar wrote to Gates.

"We respectfully and urgently request that you immediately order the prison camp's commander to cease all force-feeding of detainees who are capable of forming a rational judgment and are aware of the consequences of refusing food."

Dawkar also cited various reports that found that force-feeding at Guantanamo Bay amounted to torture and violated several US Supreme Court holdings and international agreements, including the Convention Against Torture ratified by the United States in 1994.

Lawyers representing Guantanamo detainees told AFP that force-fed prisoners were masked and strapped to a chair twice a day and were force fed protein-rich liquids through tubes inserted in their noses. The lawyers said the practice amounted to torture.

"Debilitating risks of force-feeding include major infections, pneumonia and collapsed lungs," said Dawkar, recalling that five detainees have died in custody at the US naval base prison.

Smith defended detainee care at Guantanamo Bay. "As always, our dedicated medical staff provides superb health care to all detainees, and they closely monitor the health of those detainees who choose to hunger strike," she said.

She argued that the ratio of one medical staff member for every two Guantanamo detainees "far exceeds US prison standards" and shows the prison's commitment "to the safe and humane care and custody of detainees in a legal, ethical and transparent manner."

US president-elect Barack Obama has stated his intention to shut down Guantanamo and Gates ordered aides last month to draw up plans for closing the facility.

The prison was opened in January 2002 to hold alleged "enemy combatants" captured by US and allied forces around the world during the so-called "war on terror."