Charge or Free Opposition Leaders, Sudan Told

Sudanese President Omar al-Bashir, shown here speaking at the National Congress Party headquarters in Khartoum in April 2012.(AP)

Human Rights Watch has called on Sudan to bring charges against or release six leading opposition figures, who were detained last month after they took part in talks calling for regime change in Khartoum.

"It appears the reason for them having been detained has to do with participating in the negotiations in Kampala," at which a charter calling for the overthrow of Sudanese President Omar al-Bashir's National Congress Party was drafted, Human Rights Watch's Jehanne Henry said.

According to Henry, the men are being held in unnacceptable conditions and have been denied access to their families or lawyers.

"This is certainly not the first time Sudan has lashed out at the opposition by detaining people," Henry added.

Detaining opposition figures was Khartoum's way of "silencing dissent," she said.

Listen to Sudan/South Sudan Human Rights Watch researcher Jehanne Henry's interview with John Tanza here:

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Jehanne Henry of Human Rights Watch speaks to John Tanza