(CNN) At least five people were killed in the Sudanese capital of Khartoum during demonstrations calling for President Omar al-Bashir's ouster Saturday, according to an opposition union of doctors, the Central Committee of Sudan Doctors.

The union updated its death toll Sunday in the wake of what could have been the biggest rally since a wave of anti-government demonstrations began in December.

"On this solemn day, when the people take a giant step towards their freedom, and the streets of the country are full of revolutionaries, the oppressor machine refuses to lay down its arms and declare its bias towards its people, to continue its defense of an unjust, deadly and corrupt gang," the union said in a post on the group's Facebook page late Saturday. "The killing of peaceful protesters will increase this revolution more steadfastness and move it forward."

Sudanese protesters waive the national flag as they march toward the army headquarters.

At least 26 people were injured in clashes with security forces and transferred to hospital. "A man in his fifties was run over by a government-owned Toyota pick-up truck, causing fractured bones in his hip and forearm," the union wrote on Facebook.

Crowds converged Saturday on the nucleus of Bashir's rule, Sudan's presidential palace and the nation's military headquarters, responding to a renewed call for protests from the Sudanese Professionals Association (SPA), an umbrella organization of doctors, lawyers and journalists that has led many of the demonstrations.

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