A former chief prosecutor for the controversial American prison camp at Guantánamo Bay has called for the prison to be closed, launching an online petition that has gathered some 60,000 signatures in less than 24 hours.

Col Morris Davis served for two years as the chief prosecutor for terrorism trials at Guantánamo. He decided to campaign for the closure of the camp in the wake of a hunger strike that now involves more than 100 prisoners, including some 21 who are being force fed to keep them from starving to death.

Davis's petition comes after President Barack Obama on Tuesday vowed to make good on a broken 2008 campaign promise to shutter the prison camp, which still houses some 166 prisoners despite more than half having been cleared for release.

Davis told The Guardian that he had been appalled at the concept of the prisoners going on hunger strike, in the light of the fact that so many of them have been kept in jail without trial for more than a decade. "As illogical as suicide seems, sitting there for the rest of their lives probably makes it look like a rational choice," he said.

The petition has been launched on online protest webste Change.org, which along with similar websites has become an increasingly powerful vehicle for social activists. In the petition, Davis states: "If any other country were treating prisoners the way we are treating those in Guantánamo we would roundly and rightly criticize that country. We can never retake the legal and moral high ground when we claim the right to do unto others that which we would vehemently condemn if done to one of us." The petition currently has attracted some 64,000 signatures.

Davis, echoing comments made by Obama, told The Guardian that Guantánamo was not serving any purpose, except for costing millions of tax-payer dollars, depriving prisoners of human rights and damaging America's image abroad. "It is the cost, the stain on the country and the ill will it creates. I cannot think of any logical upside to Guantánamo," Davis said.

Davis was involved from 2006 to 2007 in military commissions at the base. He resigned in protest at the appointment of senior officials in his chain-of-command who had supported the use of evidence obtained by the use of waterboarding. During his time there, charges were successfully brought against several senior terrorist suspects including the Australian David Hicks and Salim Hamdan, who was Osama bin Laden's driver.

US military guards at Guantánamo Bay. Photograph: Brennan Linsley/AP

The hunger strike has rocked the prison camp for more than two months and forced the issue of the continued confinement of the prisoners back into the global media spotlight, creating headlines across the US. Military medical reinforcements have now arrived at the isolated base, on the island of Cuba, to help with force-feeding the prisoners. Recently, violent clashes broke out as guards attempted to break the resolve of those refusing food by moving detainees into single cells. That action saw US troops fire four "less-than-lethal" rounds on inmates, resulting in several injuries.

In addressing the issue, Obama warned that the existence of the camp more than a decade after the 9/11 terrorist attacks was "… a lingering problem that is not going to get better. It is going to get worse. It is going to fester." He vowed to go to Congress and win Republican support to try to get Guantánamo closed – a process that has failed before, angering human rights activists who claim the president can act unilaterally to take steps to free many of the inmates who have been already cleared, or transfer others for trial in the civilian courts system.

Many groups, such as the American Civil Liberties Union, have asked Obama to appoint a senior official to tackle the problem and to begin transferring prisoners immediately. They have been joined by some leading figures in his own party. The powerful Dianne Feinstein, who heads the Senate intelligence committee, has written to the Obama administration asking for it to "renew its efforts to transfer 86 detainees" who have been cleared by a review board to be moved. Fifty-six of those men are from Yemen but an Obama administration moratorium on transferring detainees to that country has effectively killed any hope of their leaving Guantánamo. The Yemeni government has requested that its citizens be returned to its territory.

In another development in the worsening crisis at Guantánamo, the United Nations human rights office said on Wednesday that force-feeding detainees was a breach of international law. "If it's perceived as torture or inhuman treatment – and it's the case, it's painful – then it is prohibited by international law," Rupert Coville, a spokesman for the UN high commissioner for human rights, told the Agence France Press news agency.

The UN's position is based on the stance of the World Medical Association, a 102-nation body, whose members include the United States, which acts as a watchdog for ethics in healthcare. In 1991, the WMA said that forcible feeding is "never ethically acceptable", even if intended to benefit the health of a prisoner.