The demonstrations broke out across greater Khartoum, with some leading to the destruction of public property like buses and gas stations. One witness saw at least six burned cars on Africa Road in Khartoum; another saw protesters throw rocks at cars and block a road with burning tires and bricks.

The government has responded forcefully. A statement by the authorities promised to act “with an iron fist” to “destructive actions.” Sudan’s police forces said 29 people, including members of the police, had died in the violence, blaming “trained elements” and “rioters.”

But activists say that at least 100 are believed to have been killed, mostly by the government, with hospitals flooded. Security and police forces have used live ammunition as well as tear gas and batons to break up the protests.

“I know two who were killed,” Moyasser said. “One was shot, and the other beaten to death.”

As the protests escalated, Internet services were shut down on Wednesday and early Thursday. The authorities said that rioters had attacked and destroyed equipment belonging to a local online provider, but activists say it was a deliberate act by the government to create a blackout on events in Sudan.

The lifting of gasoline subsidies was the latest step in the difficult economic adjustments Sudan has experienced since South Sudan became independent two years ago, taking with it nearly 75 percent of the oil revenue the two countries once shared. Inflation has reached nearly 40 percent, and the value of the Sudanese pound has spiraled downward.