Sudanese protesters use burning tyres to erect a barricade on a street, demanding that the country's Transitional Military Council hand over power to civilians, in Khartoum, Sudan on June 3, 2019 STRINGER / REUTERS

Khartoum, Sudan -- Sudanese security forces attacked a protest camp in the capital Monday, opening fire and torching tents as they largely cleared away the weeks-old sit-in aimed at pressuring the military to yield power, protest leaders and witnesses said. Protest leaders said at least 13 people were killed and announced they were suspending talks with the military regarding the creation of a transitional government.

The Forces for Declaration of Freedom and Change, which represents the protesters in transition negotiations, said Monday that protesters were unable to evacuate "the bodies of our martyrs." It said hundreds of people had also been wounded.

The leaders called for an open general strike and civil disobedience, and for the international community "not to recognize the coup."

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The leading opposition Umma Party called for people to set up other sit-ins, both in the capital and across the country, saying the military's raid showed it is standing in the way of "the Sudanese revolution."

In videos posted online amid the early morning assault, civilians were seen running through streets lined with sit-in tents, heads down, as the sound of gunfire filled the air. Smoke rose from the area.

"Wounded people are lying on the ground the reception area as there are not enough beds," said Azza al-Kamel, a doctor at the Royal Care hospital near the sprawling sit-in area outside the military headquarters in the capital, Khartoum.

By mid-day, security forces controlled almost the entire camp, pushing out protesters and sealing off the nearly one square mile area, two protesters said. "We are out and cannot get in," said Hisham Shalbi, a protest leader. They said only a few small pockets of protesters in the area remained.

The camp has been the epicenter of a protest movement that succeeded in forcing the overthrow of Sudan's longtime strongman Omar al-Bashir in April. As CBS News' Iliana Hagenah reported, women have been at the forefront of the protests, and have suffered for it.

After the military removed al-Bashir and seized power, tens of thousands of protesters remained in the camp and other protest sites, saying an end to his 30-year rule was not enough and demanding a speedy transition to civilian rule.

Protest leaders and military officials have been negotiating over the makeup of a transitional government, as protesters called for "limited military representation" in a sovereign council that would lead the country as it transitions to civilian rule over three years.

Both sides have been split over the makeup and leadership of the council, with the ruling generals refusing to relinquish power.

Reaction from abroad

Protest leaders urged supporters to rush to the site and called for civil disobedience. The embassies of the United States and Britain expressed concern about reported attacks on civilians.

The U.S. Embassy in Sudan called on Sudanese security forces to stop what it said were "attacks against protesters and other civilians." The embassy said via Facebook that apparent attempts to move against the protest camp in the capital are "wrong" and that it holds the country's Transitional Military Council responsible for the attacks.

Ifran Siddiq, the British ambassador in Sudan, said he was "extremely concerned" by the heavy gunfire he had heard from his official residence in Khartoum and the reports that Sudanese security forces were attacking the protest sit-in site. "No excuse for any such attack," he said on Twitter.

The chairman of the African Union Commission strongly condemned the violence and urged the country's Transitional Military Council "to protect the civilians from further harm." The statement released Monday by Moussa Faki Mahamat called for an immediate and transparent investigation into the reported deaths and injuries.

Mahamat urged "utmost restraint" and called for civilians' rights to be respected. He urged international partners to "reinforce common efforts towards the immediate cessation of the violence."