Thousands of doctors in Egypt have staged a rare protest against police abuses after accusations that two doctors were beaten up by policemen in a Cairo hospital.

The doctors’ union also voted to offer free services in public hospitals and to call a partial strike in two weeks time unless the officers involved are held accountable, measures are taken to protect medics from police intimidation and the health minister submits his resignation.

At the headquarters of the doctors’ union, known as the Egyptian Medical Syndicate, medics on Friday chanted “strike” and raised banners that read: “dignity for doctors.”

“I am the doctor, who is going to stitch my injury?” read one banner raised by a young female doctor. Next to her a medic raised a sign that depicted a rifle shooting at a white doctor’s coat together with the caption: “police are thugs.”

Such public protests rare under Egypt’s President Abdel-Fattah el-Sissi, where voices of dissent are largely silenced.

The demonstration came in response to a 28 January assault on two doctors in Cairo’s Matariya hospital. According to online and televised testimonies of the doctors who came under attack, the incident took place after one of the doctors described the cut on the officer’s forehead as “simple” and said it didn’t require stitches. The policeman then attacked the doctors, before a colleague joined him, pulled out a gun and began to threaten the hospital staff.

The two policemen were later joined by more officers from a nearby police station. They dragged the two doctors into a bus to take them to a police station. On the way to the vehicle, one policeman stomped on a doctor’s head with his boots.

One of the doctors involved is Moamen Abdel-Azzem, who said he filed an official complaint at the police station. He said he later withdrew his complaint for fear of arrest after the police officers filed a counter-complaint accusing the medics of beating them up.

The general prosecutor has ordered an investigation into the incident and on Wednesday, 13 days after the assault, nine policemen were questioned and two were detained. All were released on Thursday pending further investigation.

“This is a turning point in our union’s history,” said Hussein Khairy, the chairman of the syndicate, addressing a cheering crowd of doctors, who filled all three floors and the roof of the union building. “We want the rule of law. Assaulters, whether they are a doctor or a policeman, must be punished.”

Doctors gather in Cairo to protest their treatment at the hands of Egypt’s police. Photograph: Hazem Abdel Hamid/EPA

Later on Friday, the union’s general assembly voted to offer free-of-charge services to all citizens as a first step in their campaign. After two weeks, if their demands are not met, they will hold a partial strike across the country.

The union said that any hospital in which doctors are assaulted will be closed. They also demanded the resignation of the health minister and that parliament speed-up the introduction of new laws to punish those who assault hospital staff, including police.

The beating of the doctors prompted anger among a large number of Egyptians, and on Friday the Arabic hashtag “#supportthedoctorssyndicate” was trending in Egypt.

The Egyptian Initiative for Personal Rights, a prominent local rights group, condemned the violence against doctors, saying that it was “a reflection of the level of police abuse of authority these days.”

President el-Sissi often portrays the security forces as national heroes battling Islamic insurgency and terrorism, but in November he offered an apology following a series of deaths in police custody, including that of a lawyer, which sparked a lawyers’ strike.