Sudan's military has dissolved the boards of all state companies and national agricultural projects, state TV said on Friday, in what appeared to be the junta's latest move to tighten control after seizing power in a coup on Oct. 25.

Under growing international and domestic pressure, the military rulers were challenged by a leading civilian group to release three political figures it said had been arrested after meeting an envoy for the United Nations.

Last week's takeover halted a power-sharing deal between the military and civilians agreed after the overthrow of long-time autocratic leader Omar al-Bashir 2-1/2 years ago, an arrangement that was meant to lead to elections by the end of 2023.

State TV gave no further details on the dissolution of state company boards.

Mediation efforts involving the United Nations have sought the release of prominent civilian figures including Prime Minister Abdalla Hamdok, who is under house arrest, and a return to power-sharing, against a backdrop of mass rallies and local protests against the military.

The Forces of Freedom and Change (FFC) coalition said three more civilians - two Sudanese Congress Party members and a senior member of a task force dismantling the Bashir government's assets - had been arrested on Thursday.

The FFC said any reports of contact between it and the military or of an imminent agreement between the military and Hamdok were untrue and "nothing but desperate efforts to sow frustration in the intrepid Sudanese street (movement)".

A source close to Hamdok said late on Thursday that talks were making progress. But many in the protest movement, which is mobilising for further demonstrations, oppose compromise with the military and are calling for full civilian rule.

The U.N. mission in Sudan condemned the reported arrests of Taha Osman Isahaq, Sharif Mohamed Osman and Hamza Farouk near its offices in the capital Khartoum and called for the immediate release of all those detained.

"These detentions hinder efforts to restore stability and a return to the path of democratic transition in Sudan and nullifies the impact of the release of four of the detained ministers yesterday," the mission said in a statement.

In Geneva, U.N. Human Rights Commissioner Michelle Bachelet called on Sudan's military leaders "to step back in order to allow the country to return to the path of progress". The U.N. human rights council agreed to appoint an expert to monitor the situation in Sudan. 

Sudan's military chief, Abdel Fattah al-Burhan, has said the army intervened because of political turmoil and the risk of civil war, and that elections will be held in 2023.

His critics accuse the army of fomenting unrest ahead of the military takeover, which they say made the risk of civil conflict more likely and derailed a transition that offered an exit from decades of isolation and internal wars.