Sudanese authorities have suspended the party of the main opposition Islamist leader Hassan al-Turabi from political activity, a Sudanese newspaper said.
Turabi was released from detention last October
Security forces have also reportedly shut down the party's headquarters.
Mr Turabi has been detained along with several opposition politicians and army officers over an alleged plot to overthrow President Omar al-Bashir.
He has denied his party - the Popular Congress Party (PCP) - was involved.
The government said the group had been "planning acts of subversion" at a number of strategic establishments.
The Sudanese ruling National Congress released a statement on state television condemning the PCP for the alleged plot.
It accusing the party of also planning "to assassinate and detain a number of prominent personalities in government and society".
"Since the release of the Turabi and the party's resumption of its political activities, fanatism, racial incitement and justification of violence and barbarism became their calls from pulpits and satellite channels," the statement said.
Mr Turabi was previously detained in 2001 after a power struggle with his former ally, President Bashir - and was released from house arrest in October last year.
Officials have also accused the alleged coup-plotters of links with rebels in the western province of Darfur.
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, Ndjamena, on Tuesday, the opposing sides are now involved in indirect talks.
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.