Controversy over the Guantánamo Bay detention camp has intensified as United Nations experts condemned the force-feeding of hunger-striking inmates by the US, and a former White House lawyer claimed that drone strikes are being used an alternative to detaining al-Qaida suspects.

With more than 100 inmates refusing food, four senior UN human rights experts and the Inter-American Commission on Human Rights called for an end to the indefinite detention of Guantánamo's inmates and for their prosecution, transfer or immediate release.

Earlier this week, Barack Obama vowed to make good on a broken promise, made during the 2008 presidential race, to get rid of the prison in Cuba. It currently holds 166 detainees despite more than half having been cleared for release. Among them is Shaker Aamer, a British resident, who has been held for more than 11 years.

Obama is likely to need the Republicans' support to close the base and rehouse the prisoners, because they control the House of Representatives.

The UN move came as John Bellinger, who worked for President Bush and drew up the first White House policy on lethal drone strikes, accused the Obama administration of overreliance on the attacks because it realises imprisoning them in Guantánamo is too problematic.

Released in response to the deteriorating situation in the camp, the UN experts' declaration points out that force-feeding hunger strikers is against international medical standards. The declaration, released through UN's Office of the High Commissioner for Human Rights, also condemned the policy of indefinite detention as "a flagrant violation of international human rights law [which] in itself constitutes a form of cruel, inhuman, and degrading treatment".

It said: "According to the World Medical Assembly's Declaration of Malta, in cases involving people on hunger strikes, the duty of medical personnel to act ethically and the principle of respect for individuals' autonomy, among other principles, must be respected.

"Under these principles, it is unjustifiable to engage in forced feeding of individuals contrary to their informed and voluntary refusal of such a measure. Moreover, hunger strikers should be protected from all forms of coercion, even more so when this is done through force and in some cases through physical violence.

"Health care personnel may not apply undue pressure of any sort on individuals who have opted for the extreme recourse of a hunger strike. Nor is it acceptable to use threats of forced feeding or other types of physical or psychological coercion against individuals who have voluntarily decided to go on a hunger strike."

The statement is signed by El Hadji Malick Sow, chair of the UN working group on arbitrary detention; Juan E Méndez, UN special rapporteur on torture; Ben Emmerson QC, UN special rapporteur on the promotion and protection of human rights; and Anand Grover, UN special rapporteur on the right of everyone to the enjoyment of the highest attainable standard of physical and mental health. It is supported by the Inter-American Commission on Human Rights.

Speaking to the Guardian, Emmerson, who has also questioned the legality of US drone strikes, said: "President Obama's announcement that he will renew and redouble his efforts to close Guantánamo as soon as possible is a highly positive indication. His administration has been committed to this policy since he was first elected, but he has been blocked by Republicans in the senate taking advantage of the toxic state of US politics … [Obama] knows, as all informed observers know, that if the hunger-strikers at Guantánamo starve themselves to death, the threat of reprisal against the US will be immediate and significant.

"Any further Republican attempts to block the president's renewed move to close [Guantánamo] will place the lives of US citizens at immediate risk all over the world."

In the US, Bellinger accused the Obama administration of overusing drones because of its reluctance to capture prisoners who would otherwise have to be sent to Guantánamo Bay.

Bellinger, who drafted the legal framework for targeted drone killings while working for George W Bush after 9/11, said he believed their use had increased since because Obama was unwilling to deal with the consequences of jailing suspected al-Qaida members. "This government has decided that instead of detaining members of al-Qaida [at Guantánamo], they are going to kill them," he told a conference at the Bipartisan Policy Centre.

An estimated 4,700 people have now been killed in some 300 US drone attacks in four countries – Afghanistan, Pakistan, Yemen and Somalia – and the question of the programme's status under international and domestic law remains highly controversial.

Bellinger, who also used to work at the state department and the national security council, insisted that the current administration was justified under international law in pursuing its targeted killing strategy in countries such as Pakistan and Yemen because the US remained at war. "We are about the only country in the world that thinks we are in a conflict with al-Qaida. We really need to get on top of this and explain to our allies why it is legal and why it is permissible under international law," he said.

A petition launched by Colonel Morris Davis, the former Guantánamo chief prosecutor, calling for its closure attracted 64,000 signatures in less than 24 hours. Writing for the Guardian, Morris said: "First, the 86 cleared detainees should be transferred out as soon as reasonably possible … Second, there are about 30 detainees the administration intended to prosecute. Third, and the most problematic, is the group of 50 or so (plus any of the 30 who do not clearly warrant prosecution in federal court) that fall in between: the indefinite detainees."

Obama said of the camp this week: "It is expensive. It is inefficient. It hurts us in terms of our international standing. It lessens co-operation with our allies on counter-terrorism efforts. It is a recruitment tool for extremists. It needs to be closed."

• This article was amended on 3 May 2013 to remove a quote attributed to John Bellinger that was in fact made by another participant at the Bipartisan Policy Centre conference. It was further amended on 3 May 2013 because it referred to Shaker Aamer as a British citizen.