The former chief prosecutor for the US government at Guantánamo Bay has accused the administration he served of operating a "law-free zone" there, on the eve of the 10th anniversary of the order to establish the detention camp on Cuba.

Retired air force colonel Morris Davis resigned in October 2007 in protest against interrogation methods at Guantánamo, and has made his remarks in the lead-up to 13 November, the anniversary of President George W Bush's executive order setting up military commissions to try terrorist suspects.

Davis said that the methods of interrogation used on Guantánamo detainees – which he described as "torture" – were in breach of the US's own statutes on torture, and added: "If torture is a crime, it should be prosecuted."

The US military, he said, had been ordered to use unlawful methods of interrogation by "civilian politicians, and to do so against our will and judgment".

Davis was speaking at a conference on human rights law at Bard College in New York state. After resigning from the armed forces, in a dramatic defection to the other side of the raging debate over conditions at the camp, he became executive director of, and counsel to, the Crimes of War project based in Washington DC. The speech was to launch the project's 10th anniversary campaign and to protest against the existence of the camp and the torture there and at so-called "black sites" run by US intelligence around the world.

"No court has jurisdiction over Guantánamo," said Davis. "Some senior civilian Bush adminstration officials chose Guantánamo to interrogate detainees because they thought it's a law-free zone where we can unlawfully… handle a very small number of cases. We have turned our backs on the law and created what we believed was a place outside the law's reach." He added that America was "great at preaching to others, but not so good at practising what we preach. There is a point when enough is enough, and you have to look at yourself in the mirror. Torture has no place in American courts."

He admitted that "for a couple of years I was a leading advocate of military tribunals", but at his first meeting as prosecutor "I told my prosecution team that I would not use any enhanced interrogation techniques – we didn't need to". However, he continued: "We had these political appointees telling us to get in there and use them."

Speaking to the Observer, he said: "The uniformed services were in opposition to what was going on. But the military was cut out of the loop. Civilian politicians excluded the military in establishing the process and then handed it to me, saying: 'Here, go make it work.' Political appointees were making the decisions and, so far as I was concerned, the methods being used were unlawful. They said: 'President Bush said we don't use torture, so if the president said it's not torture, who are you to say it is?' " At first, said Davis, "the Bush administration didn't want civilian lawyers involved. They didn't even want the Red Cross on the island."

Davis, an expert on the law of war, and former judge advocate for the US Air Force, said that prisoners at Guantánamo have "fallen between" the conventions and rules governing prisoners of war. He questioned the notion of a "war on terror", saying: "Prisoners of war are supposed to have been captured on the battlefield. Abducting people off the streets of Indonesia and other places far from Afghanistan is pushing the envelope on what is a battlefield. The whole world is in essence the battlefield."

After his resignation in 2007 and retirement in 2008, Morris was officially deemed to have acted "dishonourably". But, he said: "The people who said I had behaved dishonourably were all political appointees. I've had no one from the military or the intelligence community who has criticised what I did."

Davis's Crimes of War project is leading pressure on the administration of President Barack Obama during Guantánamo's 10th anniversary, with firm reminders of Obama's unequivocal pledges to abolish military commissions and close the camp. Professor Thomas Keenan, the head of the Bard College human rights programme, which staged the conference, said: "The president campaigned on a pledge to close down the jail at Guantánamo Bay, and to end the use of military commissions to try its inmates. How is it possible that, two years after he was elected, there are still more than 150 prisoners there, and this November, one of them will go on trial before one of those very commissions?"

The 10th anniversary of the executive order will come four days after the arraignment on 9 November of Saudi-born former millionaire Abd al-Rahim al-Nashiri, accused of masterminding the attack on the USS Cole that killed 17 US sailors in 2000. The trial is the first to be held at Guantánamo in which the government will seek the death penalty.

But lawyers for al-Nashiri, who claim he was tortured at a "black site" in Poland, will present a motion arguing that the trial is meaningless, since the government has said it will not necessarily release the accused even if he is acquitted.

Davis said he thought the handling of terrorist suspects should proceed "one step at a time, and the first step is to close Guantánamo". Trials could then be moved to the federal courts.