Three Sudanese opposition members were detained after police forcibly dispersed a rally demanding the release of other opponents of the regime held for several weeks, their leader said on Sunday.
"We dispersed but after I left the place... three young men were arrested," Farouk Abu Issa, head of the opposition alliance, told AFP.
He said they had rallied on Saturday in support of six members of opposition parties detained for their connection with a conference in Kampala, Uganda, which led to a charter for toppling the 23-year regime of President Omar al-Bashir.
"There were hundreds of women and men and children. The families of some of the detainees were there," Issa told AFP.
He said they gathered in Khartoum's twin city of Omdurman at the family home of Sudan's first prime minister, Sayyid Isma'il al-Azhari.
"After we finished we went out of the house... When we were standing there raising banners the police came and used tear gas, very excessively," said Issa, who represents more than 20 opposition parties.
His alliance, along with community activists, agreed in January to the New Dawn charter with insurgents from Sudan's Darfur, South Kordofan and Blue Nile areas.
The pact calls for regime change using both armed and peaceful means, though the political opposition says it remains committed to a non-violent transfer of power.
One month ago US-based Human Rights Watch said Sudan should charge or release the six detained opposition members.
A similar call came from the United Nations independent expert on human rights in Sudan, Mashood Adebayo Baderin.
The New Dawn pact, which has not been formally approved by senior opposition leaders, proposes replacing Bashir's administration by a "democratic federal state... based on equality," with a separation between religion and government.
Urging such a separation is a violation of the law, as is linking up with the rebels, senior ruling party official Rabbie Abdelatti Ebaid said earlier.
Sudan has faced scattered youth-driven protests with Arab Spring-inspired calls for the downfall of the government.