Pro-democracy groups began two days of strikes and civil disobedience in Sudan on Tuesday, a day after security forces fired live rounds and used tear gas to disperse protesters in some of the deadliest clashes since a military coup last year.

At least seven people were killed and hundreds injured in clashes on Monday as security forces repelled crowds attempting to advance on the presidential palace in Khartoum. The standoff marked a major escalation in tensions between the coup leaders and the growing protest movement, as...

Pro-democracy groups began two days of strikes and civil disobedience in Sudan on Tuesday, a day after security forces fired live rounds and used tear gas to disperse protesters in some of the deadliest clashes since a military coup last year.

At least seven people were killed and hundreds injured in clashes on Monday as security forces repelled crowds attempting to advance on the presidential palace in Khartoum. The standoff marked a major escalation in tensions between the coup leaders and the growing protest movement, as diplomatic efforts to end the unrest faltered.

Protests, sometimes involving tens of thousands of people, have frequently broken out in the Sudanese capital after the country’s generals toppled a hybrid military-civilian administration that had held power after the ouster of Islamist autocrat Omar al-Bashir in 2019.

The protests have spiraled into a broader outpouring of grievances against the military. The protest leaders have accused generals of mismanaging Sudan’s economy and squandering proceeds from the country’s gold and oil. The military leaders deny the accusations.

Sudan’s military sovereign council on Tuesday accused the protesters of violent conduct and said the police had acted with restraint during Monday’s clashes. Last week, the police said that protesters had stabbed to death a police general, the first high-profile fatality among the security forces.

More than 70 protesters have been killed and thousands of others detained since Gen. Abdel Fattah al-Burhan took over in October, with the unrest spreading from Khartoum to nearby adjoining cities. The strike marks a further rise in pressure on his government, with protest leaders urging followers to barricade city streets.

Union leaders urged teachers, port workers and civil servants to stay away from work. Troops, riot police and members of the paramilitary Rapid Support Forces patrolled bridges and key intersections in Khartoum, witnesses said.

Central Committee of Sudanese Doctors, which deploys medical emergency teams during protests, said all medical workers would withdraw from hospitals operated by the military, police and security on Tuesday and Wednesday.

An umbrella group of protesters, the Forces for Freedom and Change, issued a statement calling for “this period of civilian disobedience be a period of gathering, uniting and preparing our revolutionary forces to fight the decisive battle to overthrow the coup.”

At least seven people were killed and hundreds were injured in clashes on Monday.

Photo: ebrahim hamid/Agence France-Presse/Getty Images

The worsening tension coincides with a visit this week by the U.S.’s newly appointed envoy to the region, David Satterfield, and Assistant Secretary of State Molly Phee, in Washington’s latest push to end the unrest. State Department spokesman Ned Price

said on Twitter that the U.S. was concerned by the escalating violence against protesters.

The United Nations, which announced mediation efforts last week to end the standoff between the military and civilian leaders, described Monday’s crackdown as unacceptable.

In November, Sudan’s coup leaders reinstated deposed Prime Minister Abdalla Hamdok to appease protesters but he resigned earlier this month after the demonstrations continued. Meanwhile, Sudan’s economy has remained in a free fall, with inflation soaring to 443% in December from 163% a year earlier. Shortages of basic commodities from food to medicine have continued to drive discontent across the country’s impoverished cities, complicating efforts to end the standoff, analysts say.

“The failure of the previous power-sharing agreement, the October coup and the subsequent bloody crackdown have hardened the stance of both sides, making the brokering of another deal extremely challenging and prone to failure,” said Maja Bovcon, Africa analyst at risk consulting firm Verisk Maplecroft.

Mr. Satterfield and Ms. Phee kicked off their push to restore order in the troubled Horn of Africa with a meeting in Saudi Arabia on Monday, where they met a group known as the Friends of Sudan that has been calling for the restoration of Sudan’s deposed power-sharing government. The U.S. delegation will also hold meetings with Sudan’s pro-democracy activists, military leaders and political figures, the state department said.

Cameron Hudson, a former chief of staff for the Office of the U.S. Special Envoy to Sudan who is now with the Atlantic Council’s Africa Center, warned however that the U.S. needs to apply more pressure on Sudan’s military leaders amid the growing unrest.

“They kill seven and tomorrow they will sit with international diplomats to discuss compromises that will keep them part of a transitional government,” Mr. Hudson said.

Write to Nicholas Bariyo at nicholas.bariyo@wsj.com