Omar al-Bashir, the ousted president of Sudan, has been jailed by the country's new military authorities.
Mr Bashir, who was forced out in a military coup following massive street protests last week, was moved to Khartoum's Kober prison on Tuesday
It was not immediately clear whether the 75-year-old former dictator would face trial or had been charged with any crime.
Mr Bashir is wanted by the International Criminal Court on charges of genocide relating to the conflict in Darfur, but the Military Transitional Council, a group of generals and paramilitary leaders that forced him aside last week, have ruled out extraditing him to face trial.
Amnesty International called for Mr Bashir to be "immediately handed over to the International Criminal Court".
"His case must not be hurriedly tried in Sudan's notoriously dysfunctional legal system. Justice must be served," said Amnesty's Joan Nyanyuki.
Mr Bashir was forced out of power in a military coup on Thursday following a wave of anti-government protests that began in December and culminated in a vast occupation of the streets near the army's headquarters building in Khartoum.
While the crowds welcomed Mr Bashir's overthrow, protest leaders have warned they will not accept a permanent military government and have remained on the streets to demand a civilian administration.
"People fear the military council will try to stay in power as long as they can. And that is not driven by any actual things that are being done now, but by fear of the past. It is what happened after both of Sudan's previous revolutions in 1964 and 1985," said an opposition source who was on the streets on Wednesday.
On Wednesday doctors in white robes marched from Khartoum's main hospital to the site of the sit-in demonstration to show solidarity with the protesters.
Meanwhile journalists held a rally outside the offices of Sudan's state news agency, widely seen as an instrument of state propaganda, to demand a change of management. The head of the state television and radio holding was already ousted on Tuesday.
Engineers are expected to hold a similar rally on Thursday.
Meanwhile, a leader of one of several armed rebel groups in Sudan ordered a three-month ceasefire.
Abdulaziz al-Hilu, leader of the Sudan People's Liberation Movement-North (SPLM-N), which has been fighting in Blue Nile and South Kordofan states, said the truce was a "goodwill gesture" and called for immediate transfer of power to civilians.