Sudan's authorities have arrested a number of opposition politicians and army officers over a possible plot to overthrow President Omar al-Bashir.
President Bashir broke with his former key ally Hassan al-Turabi several years ago
All the detained politicians are thought to be supporters of the Islamist Popular Congress Party.
The PCP confirmed six senior officials were arrested on Sunday, but denied involvement in any alleged plot.
The detained officers and officials are also being linked to the uprising in the western Darfur region.
The Popular Congress Party leader, Dr Hassan al-Turabi, has denied that his party was involved in the incident.
He told the BBC's Focus on Africa programme that there had been "tension within the army" but there had not been an attempt to overthrow the government.
Turabi remains an influential figure in Sudan
He said he felt the government was trying to aggravate the situation to prepare the ground for his arrest and to ban the PCP completely.
Al-Jazeera TV says 27 people have been arrested by the authorities.
The BBC's Alfred Taban in Khartoum the city's former governor, Badr-Eldin Taha has gone into hiding, accused of supporting the Darfur rebels.
Peace talks over the Darfur crisis failed to start as scheduled last week. They are due to get under way shortly in Chad.
Thousands have been displaced by the fighting in Darfur
Hundreds of thousands of civilians have been displaced, with more than 100,000 fleeing across the border into Chad.
The Sudan Liberation Movement (SLM) and Justice and Equality Movement (Jem) rebels say the government has been oppressing blacks in favour of Arabs.
The United Nations humanitarian co-ordinator for Sudan, Mukesh Kapila, said that government-backed Arab militias have been systematically raping and killing in Darfur.
The fighting in the west of Sudan has intensified as government peace talks to resolve the 20-year war with southern rebels near an end.
The UN is concerned this conflict could undermine the talks which are taking place in Kenya.