The United States government has been labelled a "serial rapist" by a man who underwent forced feeding in public to protest against the treatment of prisoners at Guantánamo Bay.

Andres Conteris had a tube inserted in to his stomach via his nose in a graphic portrayal of how some inmates are treated during on hunger strike at the United States prison for suspected terrorists.

Conteris, 52, called it the "most painful experience of my life" after undergoing the procedure outside an appeal court in Washington DC to highlight the practice, which critics claim violates human rights.

His protest came as the US Court of Appeal mulled a lawsuit against force feeding.

Conteris has also stopped eating food and now consumers only water in a campaign which has lasted 106 days and caused him to lose 57lbs in weight.

Speaking at the event, he said: "They [detainees] are tortured because they do not give their consent. And without giving consent I would call this - if it were a sexual kind of analogy, it would be rape. And am I calling the Pentagon rapists? "No! I'm calling them serial rapists."

The procedure of force-feeding is known as nasogastric intubation and is employed on 16 detainees at Guantánamo Bay who have refused to eat food since last February.

Conteris described the procedure as "agony."

He said: "When the tube is gone in, at times it has blocked my capacity to breath. It felt like constant agony and it is fire in your throat. It is a burning sensation.

"And every time you try to speak, if the tube is put very near the vocal cords, which sometimes it is and sometimes it isn't, every word you speak is agony. And every time you swallow it is absolutely excruciating."