Cairo - Sudan's National Intelligence and Security Service has announced the release of all political prisoners across the country, state news agency SUNA reported on Thursday.
The announcement came after Sudanese sources said President Omar al-Bashir had been forced to step down after three decades in power.
Government sources and the minister of production and economic resources in North Darfur, Adel Mahjoub Hussein, told Dubai-based al-Hadath TV that Bashir had stepped down and consultations were taking place to form a ruling military council.
Sudanese sources told Reuters Bashir, 75, was deposed by the army and was at the presidential residence under "heavy guard".
The military will make an announcement soon, state television said as troops deployed around the defence ministry and on major roads and bridges in the capital.
Soldiers stormed the headquarters of Bashir's Islamic Movement, the main component of the ruling National Congress Party, a Reuters witness said.
Thousands of people flocked to an anti-government protest outside the defence ministry, while huge crowds took to the streets in central Khartoum, dancing and chanting anti-Bashir slogans.
Protesters outside the defence ministry chanted: "It has fallen, we won."
One protester, speaking to Arabiya TV, said reports were circulating that Bashir's deputy and Defence Minister Awad Mohamed Ahmed Ibn Auf would replace him, but this was unacceptable to the demonstrators.
"We expect good news, joyful news that we have awaited for 30 years," demonstrator Nadine Ala al-Din said.
Mohamed Adam, 44, said: "We will not accept Bashir's aides as part of the new situation. Those people have killed protesters."
Kamal Omar, a 38-year-old doctor, said a military government would not be acceptable. "We will continue our sit-in until we prevail".
State television and radio played patriotic music, reminding older Sudanese of how military takeovers unfolded during previous episodes of civil unrest.