(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.

Security forces made at least two attempts to disperse the crowds, firing teargas on protesters amassing in surrounding streets, but the sheer number of people made the demonstration difficult to disperse, eyewitnesses said.

Demonstrators in the presidential compound in the capital Khartoum.

CNN could not independently confirm the size of the crowd, but the SPA estimated that hundreds of thousands of protesters had gathered in front of the compound. Because of the nature of the protests, Khartoum officials and police are not commenting publicly on the numbers.

After "limited clashes" with protesters, the authorities withdrew, according to a local journalist who we are not naming for their security. The forces outside the general command of the Sudanese Armed Forces have so far stayed in their positions, the source told CNN.

Demonstrators planned to maintain their presence outside the presidential compound, but it was unclear how this show of resistance would play out as night fell, the local journalist told CNN. Many protesters brought mattresses and blankets as they settled in for the evening. Local businesses and tradesmen were distributing free food and water to demonstrators staging a sit-in in the streets, multiple eyewitnesses told CNN.

A solidarity demonstration was held in New York City Saturday by members of the Sudanese community. Participants listened to speakers, watched traditional dances, and chanted slogans like "Just go" and "Al-Bashir to ICC," a reference to the charges of crimes against humanity, including genocide, Bashir faces with the International Criminal Court.

"He killed so many people in Sudan and Darfur," one demonstrator told CNN. "The situation is getting very bad -- a lot of people dying. And they are torturing so many people. So we are here to protest that and to ask the international community to stand with the Sudanese people."

Since protests began in December, Sudan's government has reported 32 fatalities, including three security personnel, but doctors and opposition activists suggest the toll is much higher.

The demonstrations, which began last year over fuel shortages and a hike in food prices, have morphed into the largest popular protests in Sudan since Bashir came to power 30 years ago.

Reports of excessive force used in a crackdown by security forces against protesters since December have been condemned by the UN's High Commissioner for Human Rights and Amnesty International.

Demonstrations are being organized and documented by multiple groups, including the SPA and a media working group, with no centralized leadership.

The groups are made up of a network of Sudanese activists, journalists, doctors and filmmakers who are documenting, archiving and sharing videos, photos and witness accounts. Taking stock of the uprising has been challenging, as Sudan has sought to censor news coverage, detaining an unprecedented number of reporters in the process.

Footage shared on social media from previous rallies has shown security forces beating protesters in the streets, firing rubber bullets and live ammunition and attacking patients and staff being treated in a hospital.

On Thursday, a bipartisan group of US senators, including Ted Cruz, Marco Rubio and Cory Booker, raised their concerns over the muted US policy response to the crackdown in Sudan in a letter to Secretary of State Mike Pompeo.

"While the long-term effects of the protests and calls for transition remain unclear, twice in Sudan's recent history -- in 1964 and 1985 -- civil protests have brought down military regimes, giving a clear example of the potential outcome of this mass movement," the senators wrote.