Zimbabweans are bracing for fresh unrest after the main opposition party unveiled plans for a series of major rallies starting this week and unions called for strike action.

Any demonstrations or industrial action will pose a new test for the ruling Zanu-PF party, which brutally suppressed a round of protests in January, leading to at least 13 deaths and hundreds of rapes and beatings.

Last month senior Zanu-PF officials said the constitution allowed the government to deploy the army to confront protesters and warned that soldiers were trained to kill. “Forewarned is forearmed,” one said, telling demonstrators to stay at home.

The opposition campaign comes as the government imposes austerity measures and attempts to launch a new currency. Millions have been hit by soaring prices of food and fuel, while foreign exchange shortages have led to a lack of vital medicines and other goods.

Nelson Chamisa, the leader of the main opposition party, the Movement for Democratic Change, said it was time to throw off “the yoke of bondage” of Zanu-PF, which has ruled for nearly four decades.

“We now need to do the work, roll up our sleeves and we, as a people, be our own liberators; be our own answers; be our own solutions,” he said.

Obert Masaraure, the leader of a union representing 30,000 teachers in impoverished rural areas, said his members were not intimidated.

“We remain in the trenches and will continue to fight … We will be on the streets very soon to push the government to address this issue,” he told the Guardian. “They are celebrating budget surpluses but they are not paying workers, there are no hospital medicines … They should be ashamed of themselves.”

Lawyers on Wednesday morning reported the overnight abduction and severe beating of a human rights activist by six unidentified armed men.

The protests, scheduled to start on 16 August, come over a year since Emmerson Mnangagwa won a closely fought election promising investment, transparency and “good days ahead” for the former British colony.

Mnangagwa took power after a military takeover ousted the veteran ruler Robert Mugabe in November 2017. Mugabe, 95, is receiving medical treatment in Singapore.

Zimbabwe is crippled by massive debts incurred during Mugabe’s rule. Photograph: Tsvangirayi Mukwazhi/AP

Zimbabwe is crippled by massive debts incurred during Mugabe’s rule and needs a multibillion-dollar bailout to prevent economic collapse. However, continuing repression and a lack of tangible political reform means there is little chance of international institutions offering major aid packages.

Though most of several hundred people detained during the unrest in January have been released, 21 activists, opposition leaders and trade unionists are facing subversion charges which could lead to lengthy sentences.

Masaraure, who has been arrested five times since December, was charged with subversion in January and rearrested in June when he failed to report to police, spending five days in prison.

“There were 54 people on the floor of one room, with one blanket. The prison [clothes] were full of lice. I got sick with a chest problem,” he said.

He says the harassment has continued. The 35-year-old says he has twice been abducted from his home in the capital, Harare, and assaulted by unidentified men who he believes were state agents, most recently in June after he organised another strike. He said eight men had taken him from his house in an unmarked car to waste ground on the outskirts of the capital where he was stripped naked, beaten with rubber whips and then left by the roadside.

“I am afraid one day I will lose my life. I am afraid for my mother, for my family. The trauma is terrible … and the government is reckless, reckless against its own people,” he said.

Zimbabwe’s president, Emmerson Mnangagwa. Photograph: Jekesai Njikizana/AFP/Getty Images

In August 2018 six people were killed when the army cleared protesters from the centre of Harare at gunpoint. Some victims who survived the shootings are seeking compensation and justice with a class action against security forces.

Lovedale Munesi, a college teacher, needs $7,000 for an operation to remove a bullet lodged near his pelvis, restricting his mobility and causing severe pain. Forced to give up work, he is now dependent on painkillers and on his relatives.

“If I don’t get assistance any time soon, there may be no hope that I will ever work again. Life is very tough now,” the 30-year-old said.

Alison Charles last saw her brother Gavin the night before he was shot dead. The 51-year-old made a living selling fish in the central market area and was hit twice in the back, probably as he and hundreds of other stallholders, shoppers and commuters ran from advancing troops.

“The money is not important. I want justice … I walked with him to school every day. He held my hand. We don’t even know the identity of the soldier who shot him,” Charles said.

Gen Anselem Sanyatwe, the commander of the unit responsible for the killings, was forced to resign by Mnangagwa, and has since been appointed ambassador to Tanzania.

Energy Mutodi, the deputy information minister, said this was “appropriate action”.

“We have an opposition that is very imaginative in trying to create anarchy and to portray the government as violent … As a young democracy we are learning but we don’t need to be punished for following our learning curve,” Mutodi said.

Sanyatwe has been placed under sanctions by the US.

Mnangagwa appointed a commission headed by a retired South African judge to investigate the killings. Its report, though critical of security forces, described police overwhelmed by a large and violent demonstration by opposition activists, leading to the army’s intervention. This account contrasts with the recollections of many witnesses and the Guardian’s own reporting at the time.

Doug Coltart, a human rights lawyer in Harare, said the impunity enjoyed by those responsible for the August 2018 killings raised serious concerns for the future.

“We can see a buildup now with government ministers normalising the idea that it is OK to deploy the army against protests and use live ammunition. By failing to deal with past atrocities, the likelihood of future atrocities is very apparent,” he said.