Sudanese security forces today fired tear gas and beat demonstrators protesting against price increases for basic goods, and a journalist was found beheaded in a further sign of rising political tensions.
The protests were organised despite calls for national unity from President Omar Hassan al-Bashir as Khartoum faces off with the international community over its refusal to allow a United Nations peacekeeping force into the war-torn Darfur region.
Riot police closed ranks in Khartoum's main streets to block any gatherings of protesters, who vowed they would not stop until their right to protest peacefully was granted.
"Today we intend to deliver our statement to the presidential palace," said Mariam al-Mahdi, spokeswoman of the Umma Party, one of the largest opposition groups. She was later arrested along with around nine other senior party officials.
Before her own arrest, Ms Mahdi said she saw at least seven man arrested in the centre of Khartoum.
In another part of the city the body of a Sudanese newspaper editor was found beheaded, a day after he was reported snatched by unknown armed men from outside his home in the capital.
Mohamed Taha was an ally of the government, which took power in a military coup in 1989.
But protesters who gathered at the morgue where his body was taken accused Khartoum of doing too little to protect a man whose views had been condemned by Sudan's powerful Islamists.
No one has claimed responsibility for the killing.
The government has imposed strict Sharia law in northern Sudan but has been opposed by some Islamist groups.
"Resign, minister, resign minister!" people in a crowd of about 200 shouted after Interior Minister Al-Zubeir Bashir Taha and Defence Minister Abdel Rahim Mohamed Hussein emerged from viewing the body and visiting Taha's relatives.
Reporters at the morgue, which was guarded by heavily armed police, said they feared for the future of journalism in Sudan.
Khartoum's deputy head of police Mohamed Naguib al-Tayyib told the state news agency SUNA that a number of arrests had been made but he later told Reuters that the police still had no idea who had committed the crime.
The killing, similar to recent beheadings in Iraq, raised spectres of a violent future for Sudan.
"This is the first time this has happened in Sudan's history and we fear this will escalate," said journalist Aziza Abdel Rahman