KHARTOUM (Reuters) - Sudanese authorities arrested 14 leaders of an opposition coalition on Saturday, a spokesman for the grouping said, as anti-government protests driven by an economic crisis continued for a fourth day in several cities.

Farouk Abu Issa, the 85-year-old head of the National Consensus Forces, one of the country’s two main opposition groupings, was among those detained after an opposition meeting in the capital Khartoum, said spokesman Sadiq Youssef.

“We demand their immediate release, and their arrest is an attempt by the regime to stop the street movements,” Youssef said, adding that Abu Issa was in poor health and had been transferred to hospital after his detention.

Officials could not immediately be reached for comment.

The arrests came on the fourth day of demonstrations, fueled by deteriorating economic conditions in cities across Sudan, in which protesters have voiced anger over corruption and some have called for an end to President Omar al-Bashir’s rule.

On Saturday, students protesting in the city of al-Rahad set fire to the ruling party’s office and other official buildings and briefly closed the main road to the capital Khartoum, about 370km (230 miles) to the north east, witnesses said.

Police used teargas to disperse protesters, witnesses said. Protesters also gathered in several eastern neighborhoods of Khartoum and in the southern city of Madani, witnesses said.

Faisal Hassan Ibrahim, an assistant to Bashir and deputy head of the ruling party, said the protests were “coordinated and organized” and that two of those killed in demonstrations in the city of al-Qadarif were from the armed forces.

“Now the Sudanese armed forces are guarding strategic locations in all Sudanese regions,” he added.

At least nine people have been killed in protests this week, according to officials and witnesses, though casualty numbers are hard to confirm.

Internet service has slowed and activists have accused the government of blocking social media to stop protesters communicating. Authorities have blamed the protests on “infiltrators”.

Bashir, one of Africa’s longest-serving leaders, took power in an Islamist and military-backed coup in 1989. Lawmakers this month proposed a constitutional amendment to extend term limits that would have required him to step down in 2020.

Sadiq al-Mahdi, leader of the opposition Umma party who returned to Sudan this week from nearly a year in self-imposed exile, backed the protests, saying they would “continue because the people are driven by collapsing services”.