Barack Obama vowed to take action to close the controversial prison camp at Guantánamo Bay on Tuesday, declaring that he did not want any of its hunger-striking inmates to die of starvation.

At a press conference in Washington, Obama said it was not sustainable to keep Guantánamo open, warning its continued existence was a "recruitment tool" for extremists. The president promised to take the issue back to Congress, which blocked his earlier attempts to fulfill a 2008 campaign promise to close the camp.

The US military bas has been rocked by a widening hunger strike that now officially involves at least 100 of the prisoners, 21 of whom are being force fed. In response to the crisis a 40-strong military medical team has arrived at the isolated base on the island of Cuba to administer treatment to keep the protesters alive.

The hunger strike is said to have begun over allegations that guards mistreated Qur'ans belonging to the inmates. That has been denied by US military officials but the strike has now come to symbolise more broader protests against the camp's existence – especially as most of the terror suspects still detained there without charge have been cleared for release.

Using strong language, Obama said he would seek again to close the detention camp, fulfilling a broken promise from his first run for the White House in 2008. "I am going to go back at this. I am going to get my team to review everything that is currently being done in Guantánamo … everything that we can do administratively. I am going to re-engage with Congress to try and make the case that [Guantánamo] is not in the best interests of the American people," he said.

Obama said he did not want the protest to end in deaths, something many lawyers for those detained have warned is an increasing likelihood. "I don't want these individuals to die," Obama said.

The strike is believed to have begun on 6 February and initially involved a minority of detainees. But the number taking part has steadily increased and the situation has rapidly worsened in recent weeks, creating headlines around the world.

Two weeks ago, guards attempted to break the resolve of those refusing food by moving detainees from communal areas and placing them in single cells, where they could be monitored more closely. That action led to violent clashes in which US troops fired four "less-than-lethal" rounds on inmates.

There are about 166 inmates at Guantánamo, of whom about half have been cleared for transfer or release. Nearly all inmates have been held without charge – some for as long as 11 years – and earlier this year the State Department office meant to deal with resettling Guantánamo prisoners was closed down. Lawyers and human rights advocates say that despair at their prospects meant that some form of protest was inevitable.

Obama said that he understood why the base had been created in the emotional reaction to 9/11 but insisted it was time to close it. "It is not sustainable," he said. "I understand that reaction. But we are now over a decade out. We should be wiser. We should have more experience in how we prosecute terrorists. This is a lingering problem that is not going to get better. It is going to get worse. It is going to fester," he said, acknowledging it was a "no-man's land" for inmates.

The only major trial to emerge from Guantánamo Bay has been a military tribunal held for alleged 9/11 mastermind Khalid Sheikh Mohammed and four others, which began last year. By contrast, Osama bin Laden's son-in-law Suleiman Abu Ghaith, who was captured earlier this year, will be prosecuted in a criminal court in New York.. That follows a more recent pattern of conducting all major terrorist trials in the civilian US judicial system. "We can handle this," Obama said on Tuesday.

It is not likely to be an easy task to shut the base's prison camp. Opposition to closing Guantánamo remains strong in many quarters, especially among hawkish Republicans. The issue is an emotional one for many Americans and also comes at a time when the country is still reeling from a recent terror attack on the Boston marathon.

In order to close the base and either release or relocate the camp's inmates, Obama is likely to need the support of Republicans who control the House of Representatives and are known for their hardline approach to national security issues. But Obama said he was ready to make the argument that the camp's closure would make America safer in the long-run, ending what has become a catastrophic blight on America's international reputation for human rights policy.

"The idea that we would still maintain forever a group of individuals who have not been tried, that is contrary to who we are. It is contrary to our interests and needs to stop," he said.

"Now that is a hard case to make because I think for a lot of Americans the notion is: out of sight, out of mind. And it is easy to demagogue the issue. That's what happened the first time it came up. I am going back it because I think it is important."

The promise of action was welcomed by campaign groups, who urged Obama to appoint someone to his administration to act immediately. But they also claimed that there was no need for the president to go to Congress to get political support.

"The president can order the secretary of defense to start certifying for transfer detainees who have been cleared, which is more than half the Guantánamo population," said Anthony Romero, executive director of the American Civil Liberties Union.