CAIRO (Reuters) - A riot erupted in a Cairo suburb on Tuesday after a policeman shot three people after an argument over the price of a cup of tea, killing one of them, the Interior Ministry and witnesses said.

Public anger over allegations of police brutality has been bubbling over the past months, with several incidents spilling over into skirmishes and protests, five years after the ministry’s officers were a major focus of the 2011 uprising.

One of the onlookers held up a bullet casing and accused the police of killing “poor” Egyptians.

A crowd quickly gathered, overturning a police vehicle and beating up another policeman at the scene, said a witness, who did not see the shooting but said he arrived at the scene in the well-to-do neighborhood of Rehab shortly afterwards.

“The Interior Ministry are thugs,” chanted the crowd in a video sent to Reuters by the witness. Around 200 people were in the crowd, according to a Reuters estimate from the footage.

Rights activists say police brutality is widespread in Egypt and that there is a culture of impunity. The Interior Ministry says abuses are isolated and incidents are investigated.

Witnesses said on social media the argument on Tuesday was over the price of a cup of tea, which was confirmed to Reuters by security sources. The video, one of several shared by the witness, showed a man lying still on the floor surrounded by angry onlookers.

The Interior Ministry said in a statement that a policeman got into an argument with a vendor over “the price of a drink” and shot him dead, injuring two others in the process.

A judicial source told Reuters the policeman shot the three men with an assault rifle and fled. The victim died from a bullet to the heart, the judicial source said.

“There are clashes between the police and locals. Security forces brought in two riot police vehicles and an armored truck and the victim’s family is here and pelting them with rocks,” said the witness who sent the video and who declined to be named for fear of reprisal.

“Security forces are retreating and promising justice but the crowd is demanding police hand over the killer.”

Anger over perceived police excesses helped fuel the 2011 uprising that ended President Hosni Mubarak’s 30-year rule and began on a Police Day holiday. Since then, police have regained their power and human rights groups say they have returned to their old ways.

Public anger against police has surged again in recent months.

In February, a policeman shot dead a driver in the street in an argument over a fare, prompting hundreds to protest outside the Cairo security directorate. There were also riots in Ismailia and the southern city Luxor over the authorities’ handling of at least three deaths in police custody in a single week in November.

Egyptian security forces have also faced scrutiny over the killing of Italian researcher Giulio Regeni in Cairo this year. Human rights groups say his death bears the hallmarks of Egyptian security agencies. Officials deny involvement.

“A hundred years of isolated incidents,” wrote one commentator on Twitter.