A long-running hunger strike by detainees at Guantánamo has worsened since Barack Obama promised action to close the controversial prison camp in a landmark speech last Thursday.

On the eve of Obama's address, there were 103 prisoners on hunger strike, with 31 being force-fed by military authorities and one in hospital. Since then, not a single prisoner has stopped their strike, and now 36 of the detainees are being force-fed to keep them alive, with five of them being hospitalised.

In telephones calls and letters to their legal representatives, detainees have also described a regime of intimidating body searches and other restrictions they say are designed to prevent them from talking to their lawyers and also to break their resolve.

However, it seems that the hunger strike is showing no signs of ending, despite several promises made by Obama to shutter the camp and release many of those who have been held there without charge for more than a decade. "The numbers of strikers are not moving downwards. Nothing has changed," said Carlos Warner, a lawyer for several detainees.

Others who work with the detainees said they feared the media spotlight would move on from the issue, despite the fact that nothing concrete has yet emerged from Obama's speech. "The hunger strike is the only reason we are talking about Guantánamo. It would be a terrible mistake by the administration to think that they have dealt with this with one speech," said Omar Farah, a lawyer at the Centre for Constitutional Rights which works with numerous prisoners who are striking.

Obama has now promised a series of measures at Guantánamo, including the lifting of a moratorium on releasing detainees to Yemen, a plan to appoint a senior official to the task of overseeing transfers, the trying those to be charged in the future within the civilian justice system, and the moving of military tribunals to US soil.

In his speech, the president also referenced the strike and portrayed Guantánamo as a moral wrong that needed to be corrected, in accord with American values and to stop harming the country's image abroad.

There are 166 prisoners currently at the base and 86 of them have been cleared for release, though US security concerns have meant there has been little recent movement to send any prisoners to their home countries or other states willing to take them. Of those 86, 56 are from Yemen, who will now theoretically benefit from the lifting of restrictions on transfers to that country.

But lawyers and human rights activists have said that they need to see firm steps taken after the speech. They point out that Obama first promised to close the base in 2008 and has repeated his desire to do so with the help of the Republican-controlled House of Representatives – something that many leading figures in the GOP have vowed to stop.

If this latest push fails, some observers say, the impact on the hunger striking prisoners' morale could be catastrophic. "In many ways, the most dangerous thing for these prisoners is to offer them hope," said Clive Stafford Smith, a British lawyer at the group Reprieve who works with numerous inmates, including the sole Briton in the camp, Shaker Aamer.

Photograph: John Moore/Getty Images

Smith and other lawyers also described harsh regime in the base, including intense body searches of prisoners seeking to make phone calls. Smith said that this appeared designed to intimidate inmates from communicating with the outside world. He reported that of the last six phone calls he had tried to place to clients, four of them had been rejected because detainees had not wanted to go through the process. Warner also said he had had recent difficulty communicating with his clients.

In a statement, Smith reported Aamer as telling him last Friday: "To describe you the humiliation … they tossed me around like a burger. Flat on my back. They started dressing me with small-size underwear."

Other detainees have made allegations that their genitals are touched during the searches and even that they have been subject to body cavity searches. "Our private parts are checked and they know is a sensitive matter for us and our religion," said Syrian detainee Abu Wael in a statement passed to the Guardian.

Wael has now filed legal papers alleging a deliberate policy of using the searches as a method of intimidation. In documents sent to a Washington DC court, he stated: "The primary manner in which this has been done has been by instituting a new search protocol that exploits the prisoners' well-known phobia when it comes to anything that might be construed as sexual contact."

That has been denied by the US military, who say searches are routinely carried out any time a prisoner moves within the camp. "We conduct detention operations in a safe, humane, legal and transparent manner. Any allegations that we are conducting strip searches and cavity searches as a condition of legal phone calls are nonsense," said spokesman Colonel Samuel House.

However, there is little doubt that the strike has been a PR disaster for the Obama administration – highlighting both its failure to fulfil campaign promises and the conditions at the camp, where scores of men are held indefinitely without charge or prospect of release.

That has been heightened by harrowing accounts of the reality of the mass force-feeding that is now being carried out on dozens of the protesters by a military medical team rushed to Cuba to deal with the crisis.

"Sometimes the person on hunger strike vomits as a result of this, which is painful. This happened to me several times when the [feeding] tube goes down from the nose to the throat and strikes the tongue," said Yemeni detainee Samir Mukbel in another statement obtained by Stafford Smith.

Others have talked of the impact that a prolonged hunger strike has on their health. Pakistani detainee Ahmed Rabbani claimed he weighed just 107lbs – down from 167lbs before the strike. "I vomit and cough blood … I have often thought of smashing my head against the wall and cracking it because of [severe pain]," he said.