The activists, including Saleh Mahmoud, a Darfuri lawyer who won a human rights award from the European Parliament, said they had their passports confiscated at Khartoum airport and were prevented from heading to the conference in neighboring Uganda.
"This is obviously a violation of our freedom," Mahmoud told Reuters. "We were told we can go to the political office of the national security force after a week to collect our passports." With him was the daughter of the last democratically elected leader of Sudan, Mariam Al-Mahdi, and another lawyer, Bukhari Ja'ali, he added.
"This conference is targeting Sudan," said a Sudanese security source, who did not give further details.
The May 31-June 11 conference will review the treaty which formed the ICC and discuss the court's impact on victims and peace and justice. The ICC has mostly focused on African conflicts whose governments referred cases, including Uganda's long-running Lord's Resistance Army rebellion.
Sudan's Darfur conflict was the first case to be referred to the court by the UN Security Council in 2005. The ICC has since issued arrest warrants for a junior government minister, an allied Darfur militia leader and last year Bashir himself, accused of war crimes and crimes against humanity.
After mostly non-Arab rebels took up arms in early 2003 accusing Khartoum of marginalizing remote Darfur, a counter- insurgency campaign drove more than 2 million from their homes.
The United Nations estimates the humanitarian crisis has killed 300,000 people.
Khartoum puts the death toll at 10,000 and rejects the ICC's jurisdiction. Bashir reacted to the arrest warrant by expelling 13 aid agencies working in Darfur, accusing them of spying for the court.
