KHARTOUM (Reuters) - Sudanese security authorities arrested several faculty members from Khartoum University on Sunday, two professors said, after they joined anti-government protests that have posed the most serious challenge to President Omar al-Bashir’s rule.

The arrests came amid fresh demonstrations in Khartoum and Wad Madani in response to a call by a coalition of professional unions to push for Bashir to step down.

Witnesses said security forces blocked professors and lecturers from coming out to protest outside the university, arresting at least eight. It was the first time the faculty of the country’s oldest and most prestigious educational institution has joined the protests since they began last month.

The rest were forced to return into the faculty club house, where security forces surrounded the building trapping about 100 professors and lecturers inside for nearly three hours.

“We demand the president of the republic to step down,” one placard read carried by the lecturers inside the club house, according to pictures posted on social media.

A police spokesman could not immediately be reached to comment.

Intermittent protests have rocked Sudan since anger over food shortages and rising bread prices erupted into demonstrations in the city of Atbara in the north on Dec. 19.

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Security forces have used tear gas on occasions, live ammunition against demonstrators and rounded up more than 2,000 people. The Sudanese government has said that 19 people were killed in the protests, including at two members of the security forces. Amnesty International has put the death toll at 37.

FRESH PROTESTS

In Sunday’s protests, witnesses said hundreds of men and women marched from three separate locations in the capital trying to reach the presidential palace in central Khartoum but were dispersed by security forces using tear gas and stun grenades.

A separate protest in Wad Madani, Sudan’s second largest city, was also dispersed by security forces using tear gas, according to witnesses.

The protests were smaller than previous demonstrations.

They are the most persistent opposition Bashir has faced since he took power in an Islamist-backed coup nearly 30 years ago.

Sudan’s economy has struggled to recover from the loss of three quarters of its oil output - its main source of foreign currency - since South Sudan seceded in 2011, keeping most of the oilfields.

The United States lifted 20-year-old trade sanctions on Sudan in October 2017. But many investors have continued to shun a country still listed by Washington as a state sponsor of terrorism, whose president is wanted by the International Criminal Court over charges of masterminding genocide in Darfur - charges he dismisses.