About 1,000 people were detained and hundreds injured -- many by tear gas -- during anti-regime protests on Friday in Sudan, an activist group said on Saturday's anniversary of President Omar al-Bashir's coup.
"Some were arrested and released," said an official from the Organisation for Defence of Rights and Freedoms.
The organisation's figures indicate a dramatic rise in the number of arrests on Friday, the 14th day of anti-regime demonstrations sparked by inflation.
"The figure of those arrested before yesterday (Friday) was about 1,000 in the whole country," said the official who asked not to be identified because of the tense situation.
Many are still being held in prisons or "ghost houses," the location of which is unknown, he alleged.
"They don't tell you where they are. You are not even allowed to ask," he said.
One of those detained is Sudanese journalist Talal Saad, who had brought some freelance photos of the protests to the AFP bureau in Khartoum on Friday.
Armed national security agents raided the bureau, ordered correspondent to delete the photos and took Saad away.
He has been unreachable for more than 18 hours.
The Organisation for Defence of Rights and Freedoms said "a few hundred" people were injured during protests on Friday. Many elderly people were affected by tear gas but other injuries came from rubber bullets, tear gas canisters, or beatings, the official said.
Activists had called for a major day of protest on Friday.
In one key disturbance, witnesses said police fired tear gas and rubber bullets to disperse hundreds of peaceful protesters who had gathered in Hijra Square beside the mosque of the opposition Umma party in Khartoum's twin city of Omdurman.
Police said the crowd numbered in the thousands.
One witness said demonstrators carried Sudanese flags and banners reading "The people want the regime to fall," a slogan used by protesters during the Arab Spring uprisings against regional strongmen over the past year.
They burned tyres and threw stones at police before running for cover, the witness said.
Similar running battles between protesters and police took place elsewhere in Khartoum, the witness added.
International criticism of Sudan's crackdown increased on Friday with Canada's top diplomat expressing concern.
"We condemn the arrests of bloggers, journalists and political activists that have taken place over the last week and call for their immediate release," Foreign Minister John Baird said.
UN High Commissioner for Human Rights Navi Pillay has urged the government to avoid "heavy-handed suppression" of protests and to immediately release those detained for exercising their rights to freedom of assembly and expression.
Britain and the United States have also sought the release of those detained for peaceful protest.
On June 30, 1989, Bashir seized power from democratically elected leader prime minister Sadiq al-Mahdi, who currently leads the Umma party.
Bashir was declared winner of a multi-party election in 2010, but observers from the European Union and the US-based Carter Centre said the ballot failed to reach international standards.
Bashir is wanted by the International Criminal Court for crimes against humanity, war crimes and genocide allegedly committed in Sudan's western region of Darfur.
He has played down the demonstrations as small-scale and not comparable to the Arab Spring uprisings in Egypt and elsewhere, maintaining that he himself remains popular.