Troops opened fire on pro-democracy protesters who flooded the streets, with at least two reported killed.

Troops fired on demonstrators outside the Sudanese army headquarters, killing at least three people and injuring more than 80 according to a doctors’ group, as pro-democracy protesters flooded into the streets of the capital, Khartoum, on Monday, after the military mounted a coup, detaining the prime minister, suspending the government and declaring a state of emergency.

The casualty figures were reported by the Central Committee of Sudanese Doctors, and other witnesses reported periodic bursts of gunfire around the city throughout the day. Nazim Sirag, a well-known pro-democracy activist, and Monim El Jak, an adviser to a cabinet minister, said they knew of at least two deaths.

The Sudanese ministry of culture and information said on Facebook that military forces had “shot live bullets at protesters rejecting the military coup in Khartoum.”

Video and photos posted on social media and broadcast on television stations showed demonstrators barricading roads, waving flags and banners, and burning tires, sending plumes of black smoke into the sky. They blocked streets with large stones and barbed wire as their processions grew. Masked protesters beat sticks against jerrycans and drums, brandished tree branches and held their phones to record the unfolding scenes.

“The people are stronger,” the demonstrators chanted. “Retreat is impossible,” they insisted, a reference to the possibility of returning to the three-decade autocratic rule of President Omar al-Bashir, who was deposed in 2019.

The U.S. Embassy said on Twitter that it had received reports that armed forces were “blocking certain areas in and around Khartoum,” and urged its citizens to “shelter in place.”

Schools, banks and business establishments were mostly closed, witnesses said, as the Sudanese Professionals Association, a pro-democracy coalition of trade unions and other groups, called for civil disobedience.

Ahmed Abusin, a 27-year-old businessman in Khartoum, said security officers had surrounded the airport and key government buildings. Gunfire could be heard, he said, as demonstrators flocked to the streets. There was no internet access and it was hard to make calls locally, he said, but no amount of restrictions would deter protesters.

“This coup has no support at all,” Mr. Abusin said in a telephone interview.

In the capital, women in colorful veils joined the protests. Some demonstrators waved the Sudanese flag, while others flashed the “V” for victory sign.

“We are challenging al-Burhan,” one woman said, referring to Lt. Gen. Abdel Fattah al-Burhan, the head of the joint civilian-military council who announced the military’s takeover and the beginning of a state of emergency.

Protesters, some whistling and shrieking, carried each other on their backs and urged a return to the civilian transition.

“We are revolutionaries. We are free,” they chorused. “We will complete the journey.”

In the city of Omdurman near Khartoum, demonstrators urged their fellow citizens to resist the military. In Port Sudan in the east, hundreds of protesters could be seen gathering before heading off into a march chanting “peaceful, peaceful.”

With the internet and phone networks severely disrupted in an apparent attempt to stifle opposition to the military’s actions, many Sudanese citizens abroad expressed concern.

“Just like millions of Sudanese in and outside of Sudan, I feel disappointed and angry,” Khalid Albaih, a political cartoonist who was about to return to Sudan, said in an interview from Doha, Qatar. He said the Sudanese people were being denied democratic freedoms.

Simon Marks contributed reporting.