The US president, Barack Obama, has ordered a suspension of the controversial Guantánamo Bay military tribunals in one of his first actions after being sworn in, yesterday.

An image of President Barack Obama is put up in the lobby of the headquarters of the US naval station at Guantánamo Bay. (Photograph: Brennan Linsley/AP) Within hours of taking office, Obama's administration filed a motion to halt the war crimes trials for 120 days, until his new administration completes a review of the much-criticised system for trying suspected terrorists.

The motion, which will suspend cases against 21 men, was filed at the direction of Obama and Robert Gates, George Bush's defence secretary, who has kept his job in the new administration.

It will be considered today by military judges hearing the cases of five men charged with plotting the September 11 attacks, and that of Omar Khadr, a Canadian who is accused of killing an American soldier with a grenade in Afghanistan, in 2002. The judges will be required to suspend the other cases as well.

The halt to the tribunals was sought "in the interests of justice," the official request to the judges said.

Moazzam Begg, the former British detainee at Guantánamo Bay, urged Obama to go further. "There is no clear statement about this being stopped and the whole process being recognised as illegal," he said.

"For myself and other former detainees, until we see something tangible happening, we are going to reserve judgment. That is because we have been here before - Bush has stated he wanted Guantánamo closed."

Human rights groups who are at Guantánamo Bay to observe this week's session of the tribunals welcomed the move.

"It's a great first step but it is only a first step," said Gabor Rona, the international director of Human Rights First. "It will permit the newly inaugurated president and his administration to undertake a thorough review of both the pending cases and the military commissions process generally.

"The suspension of military commissions so soon after President Obama took office is an indication of the sense of urgency he feels about reversing the destructive course that the previous administration was taking in fighting terrorism."

Jamil Dakwar, director of the human rights programme at the American Civil Liberties Union, said it was a positive step but noted "the president's order leaves open the option of this discredited system remaining in existence".

Clive Stafford Smith, the human rights lawyer who has represented Guantánamo suspects, said: "It's great isn't it? There is no doubt it will stop the practices at Guantánamo. After all, Obama is now the commander-in-chief." Speaking on BBC Radio 4, he added: "It's going to take some work but what he [Obama] is looking at I think here is a very clear-cut distinction between this administration and the last," he said.

Relatives of victims of the September 11 attacks, who were also at the base to observe the hearings, have said they oppose any further delay in the trials of the men charged in the case.

The requested suspension came on the day a military judge adjourned the war crimes court just before Obama was sworn in, noting that the future of the commissions were in doubt.

Obama has pledged to close the Guantanamo Bay detention camp, which holds 245 men, and had been expected to suspend the widely criticised tribunals.

The president's nominee for attorney general, Eric Holder, has said the military commissions lack sufficient legal protections for defendants and that they could be tried in the US.