Sudan's authorities have arrested the opposition Islamist leader Hassan al-Turabi over an alleged plot to overthrow President Omar al-Bashir.
Turabi was released from detention last October
A number of opposition politicians and army officers have also been detained.
Mr Turabi has denied his party was involved in any plot. His wife said he was arrested at his home overnight.
Those detained are also being linked to the uprising in the Darfur region. On Wednesday talks between the government and the Darfur rebels got under way.
Although the government delegation and a number of rebel representatives failed to appear at the opening ceremony in the Chadian capital, N'Djamena, on Tuesday, the opposing sides are now involved in indirect talks.
Mr Turabi's wife Wisal al-Mahdi said the security forces arrested her husband at home at 0120 local time (0020 GMT) on Wednesday.
"They came in about seven cars and were very aggressive but they did not say why they were arresting my husband," she told the BBC's Network Africa programme.
"My son went along with them and he is waiting outside the security office to see what will happen."
She said the family is very angry about Mr Turabi's arrest and accused the government of denying him the right to express himself.
"My husband is against the killing of innocent people in west Sudan but he cannot take up arms against the government," Mrs al-Mahdi said.
Mr Turabi's Popular Congress Party confirmed six senior officials were arrested on Sunday.
President Bashir broke with his former key ally several years ago
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.
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.
The opposition leader is a former ally of Mr Bashir, who came to power in an Islamist-backed coup in 1989.
Mr Turabi was previously detained in 2001 after a power struggle with Mr Bashir - and was released from house arrest in October last year.
Al-Jazeera TV says 27 people have been arrested by the authorities over the possible plot.
The BBC's Alfred Taban in Khartoum says the city's former governor, Badr-Eldin Taha has gone into hiding, accused of supporting the Darfur rebels.
Hundreds of thousands of civilians have been displaced, with more than 100,000 fleeing across the border into Chad.
Thousands have been displaced by the fighting in Darfur
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.