Barack Obama has requested the suspension of all military tribunals at Guantanamo Bay, in his first major act as the new US president.
The request would halt proceedings in 21 pending cases, including one against five men accused of plotting the 11 September 2001 attacks.
The halt would give Mr Obama time to review the tribunal process.
The new president is beginning his first working day by meeting economic advisers and top military commanders.
Most of his cabinet is in place but several key posts are still to be confirmed.
Mr Obama himself attended inaugural balls late into Tuesday night, as America marked the arrival of its 44th president and first African-American leader.
‘Ideals versus safety’
Barack Obama has repeatedly promised to close the Guantanamo Bay detention camp, where some 250 inmates accused of links to terrorism remain.
Just hours after taking the oath of office on the steps of the US Capitol, he moved to halt the controversial process of military tribunals.
The two-page document, ordered jointly by Mr Obama and the US Department of Defense, seeks a 120-day suspension of trials and will be heard by two tribunal judges on Wednesday.
The delay would “permit the newly inaugurated president and his administration time to review the military commission process”, the document said.
The legal process has been widely criticised because the US military acts as jailer, judge and jury, says the BBC’s Jonathan Beale in Washington.
And in his inaugural address on Tuesday, Mr Obama emphasised the idea of respect for justice and the rights of the individual, rejecting “as false the choice between our safety and our ideals”.
Cabinet hearings
On his first full day in the Oval Office, Mr Obama is due to meet top national security officials as he takes over as commander-in-chief.
He was also due to conduct a video conference with US military chiefs in Iraq and Afghanistan, officials said.
In his inaugural address, the new president spoke of his desire to usher in a new era of peace.
“We will begin to responsibly leave Iraq to its people, and forge a hard-earned peace in Afghanistan,” he pledged.
The US Senate has already approved six members of his Cabinet, including Janet Napolitano as homeland security secretary and Steven Chu as energy secretary.
However, Hillary Clinton’s approval as secretary of state was postponed after a Republican senator demanded a debate beforehand about foreign donations to a foundation headed by her husband, former President Bill Clinton.
That debate is due on Wednesday and Mrs Clinton’s nomination is now expected to be confirmed in a vote immediately afterwards.
Timothy Geithner, the nominee to head the treasury department, is due to face the Senate finance committee on Wednesday to explain his initial failure to pay payroll taxes he owed while working for the International Monetary Fund.