Sudanese authorities have arrested the head of the opposition Congress Party, three weeks after the arrest of another opposition leader sparked violent anti-government protests.
Congress Party chief Ibrahim al-Sheikh was arrested on Sunday on charges of spreading "harmful lies", after he made a speech criticising the government's handling of the Darfur crisis and a surge of violence.
The party's general secretary, Abdel Kayoum Awad, told the Reuters news agency that al-Sheikh was charged with "undermining the constitutional regime, spreading lies and threatening peace."
Sheikh could face the death penalty if found guilty, Awad said.
Former Prime Minister al-Sadiq al-Mahdi, who heads the opposition Umma Party, was arrested last month after he reportedly accused the Rapid Support Forces (RSF) of rape and other civilian abuses in the Darfur region of western Sudan.
The arrests are likely to hurt national dialogue talks that were called by President Omar al-Bashir in order to ease tension among Sudan's political parties ahead of next year's parliamentary and presidential polls.
Opposition parties in Sudan have voiced concern about the government's mismanagement of Darfur, accusing it of killing civilians during a recent surge of violence in the region.
Law and order has collapsed in much of Darfur, where mainly African tribes took up arms in 2003 against the Arab-led government in Khartoum, which they accused of discriminating against them.
The conflict has killed more than 300,000 people and displaced about two million, according to the United Nations.
Bashir has a pending arrest warrant against him from the International Criminal Court on charges of masterminding genocide and other war crimes in Darfur.