Sudanese police broke up several protests held after Friday prayers, as security agents arrested a top opposition leader after calls for more demonstrations against a rise in bread prices.
Angry crowds have taken to the streets in Khartoum and other cities since December 19 after a government decision to hike the cost of bread.
Nineteen people have been killed so far in the protests, the government said.
Police fired tear gas at hundreds of worshippers who staged demonstrations after Friday prayers in several cities, including Khartoum and its twin city of Omdurman on the west bank of the Nile, witnesses said.
Protests were also staged in Port Sudan, Atbara and Madani, witnesses said, adding that several of them were later broken up by anti-riot police.
Crowds of worshippers chanted "Freedom, Peace, Justice" as they poured out of a mosque in Omdurman belonging to main opposition National Umma Party, a witness said.
But they were quickly confronted by anti-riot police who fired tear gas to break up their demonstration, the witness added.
Photographs posted by activists on social media networks showed thick plumes of smoke rising from some neighbourhoods in Khartoum as protesters burnt garbage and tyres.
The protests came as opposition groups called for more anti-government rallies to be held over the next few days.
A group of opposition parties met late on Thursday and agreed to "push for more protests" in the coming days, the Sudanese Communist Party said in a statement.
Several opposition party members have been arrested amid a crackdown on demonstrations.
Omar el-Digeir arrest
The opposition Sudanese Congress Party said that a few hours after protests began on Friday its chief Omar el-Digeir was arrested by security agents.
"He has been taken to an unknown location," the party said in a statement.
Sudanese Writers' Association said that well known poet Mohamed Taha had also been arrested on Tuesday after he participated in a protest in Khartoum.
"We don't know his whereabouts," the association said.
The Sudanese journalists network said that two journalists were detained.
Among those killed in the protests — which first erupted in towns and villages and later spread to Khartoum — were two security personnel, according to the government.
Most died during "incidents of lootings", while 219 people were wounded, said government spokesman Boshara Juma, adding that no deaths had been reported in Khartoum so far.
Late on Friday a minister said police had captured a group belonging to a prominent rebel leader from from war-torn Darfur that had plans to "kill demonstrators".
"Police captured 10 people belonging to SLA/Abdel Wahid group along with 14 Kalashnikovs and 1,000 bullets," Minister of State for Information Mamoun Hassan said.
He said police also confiscated some computers from the group.
"Documents inside the computers reveal that these people had plans to kill demonstrators," Hassan said.
United Nations expert on human rights in Sudan, Aristide Nononsi, expressed alarm at the violence.
"I strongly urge the Sudanese security forces to exercise the utmost restraint to avoid the escalation of violence and take immediate measures to protect the right to life of the demonstrators," he said in a statement.
Crowds of people have rallied since last week after the government raised the price of a loaf of bread from one Sudanese pound to three (from about two to six US cents).
Although most protests are against the high cost of living and food prices, some protesters have also adopted the slogan used in the 2011 Arab Spring — "the people want the fall of the regime".
Sudan is facing an acute foreign exchange crisis and soaring inflation, despite Washington lifting an economic embargo in October 2017.
Inflation is running at 70 percent and the Sudanese pound has plunged in value, while shortages of bread and fuel have regularly hit several cities.