Sudan's powerful state security service has demanded a ban on two major political parties whose members joined armed rebels in calling to overthrow the government, an opposition leader said on Tuesday.
The proposed ban applies to the Umma Party, led by former prime minister Sadiq al-Mahdi, and the Popular Congress of Sudan's veteran Islamist leader Hassan al-Turabi.
Intelligence chief General Mohamed Atta al-Moula also called for a ban on the smaller Communist Party, according to a letter purportedly signed by him which the Popular Congress presented at a news conference.
"With this step the government are preparing to ban the parties," Kamal Omar, head of political affairs for the Popular Congress, told reporters.
Umma, Popular Congress and the communists joined other opposition parties and activists who signed the New Dawn charter, which calls for regime change, last month in Kampala, Uganda.
Party representatives endorsed the document, but it has not yet been formally approved by senior leaders, who say they are still studying it.
The charter would commit the political opposition and the armed Sudan Revolutionary Front (SRF) to toppling President Omar al-Bashir's 23-year Islamist regime.
They propose to replace it with a "democratic federal state... based on equality," with a separation between religion and government.
"By signing this document they are supporting SRF and its armed struggle against the constitutional regime," said Moula's letter which was addressed to Sudan's Political Parties Affairs Council, the body that registers parties.
The political opposition says it remains committed to peaceful regime change.
The Parties Affairs Council, in a separate letter presented by Omar, gave the political organisations one week to clarify their position.
Omar said the Council is acting outside its jurisdiction and should file a case with the Constitutional Court.
SRF includes rebels who have been fighting for the past decade in Sudan's Darfur region, as well as other insurgents active in South Kordofan and Blue Nile states.
In December the security service detained Farouk Abu Issa, the head of the opposition political alliance, for two days without charge.
Upon his release, Issa said the government fears rising popular discontent in a nation which is in economic crisis.
Sudan has faced scattered youth-driven protests with Arab Spring-inspired calls for the downfall of the government.
The official SUNA news agency said Khartoum has complained about Uganda to the Organisation of Islamic Cooperation, partly over Kampala's "support" for the New Dawn document.
OIC leaders are meeting in Cairo on Wednesday.
Uganda backed South Sudan during Sudan's 22-year civil war which ended in a peace deal that led to the South's independence in 2011.
Sudan accuses South Sudan of backing the rebels in South Kordofan and Blue Nile.