Khartoum:
The arrest of Sudan's former prime minister and leading opposition figure Sadiq al-Mahdi undermines talks aimed at finding a way out of the country's multiple crises, observers have said.
Mahdi was arrested for alleged treason by agents of the National Intelligence and Security Service (NISS) from his home on Saturday night, officials of his Umma Party said.
Prosecutors questioned him on yesterday at the Khartoum-area Kober Prison where he is being held, Umma's secretary general Sara Najdallah, told reporters.
The arrest came after Mahdi reportedly accused a counter-insurgency unit, the Rapid Support Forces (RSF), of rape and other abuses of civilians in Darfur.
"We are deeply concerned. This isn't the way to do national dialogue," a British embassy spokesman said.
Magdi El Gizouli, a fellow at the Rift Valley Institute, said yesterday Mahdi's detention reflects a power play by elements of the state security service who "don't care" about the impact on the dialogue initiated by President Omar al-Bashir.
"The political system in Sudan is the rule of the military and the security," Gizouli told AFP.
Yesterday NISS, which has authority over the RSF, announced in a notice to local journalists that the unit has been ordered deployed around the capital Khartoum.
Umma and the Popular Congress opposition of veteran Islamist Hassan al-Turabi were key targets of Bashir's dialogue which, a senior opposition figure has said, might have led to a coalition government.
Following Mahdi's arrest, Najdallah said her party was withdrawing from the dialogue and accused the government of going back to "square one."
She announced an "alert" for Umma supporters to peacefully oppose their leader's arrest.
Hundreds of them gathered yesterday at Umma's Khartoum-area headquarters, an AFP reporter said.
They carried signs saying: "No dialogue with state security" and "Sadiq al-Mahdi's opinion is the opinion of the people."
The Bashir regime has faced mounting challenges since the separation of South Sudan three years ago.
In January the president appealed for a broad national political dialogue and "renaissance" focused on peace in the war-torn, impoverished country.