Warsaw: A woman wounded three people inside an educational institution in Poland's capital, Warsaw, on Saturday, police say, in the third attack at a school in less than a week.

The school was open on Saturday, and the victims were submitting papers at the school office when they were attacked, police said.

The attack came after police on Saturday said they detained 76 people across Poland and checked nearly 50,000 schools nationwide as part of efforts to prevent further violence following two school attacks earlier in the week.

The suspect on Saturday used a “dangerous object” to attack a 17-year-old girl and also wounded two other people, aged 17 and 24, Jakub Filipiak, a spokesman for Warsaw police, told The Associated Press. None of the wounds were life-threatening. The suspect was in custody.

On Wednesday, a 19-year-old student at a vocational school in the Mazovian province in central Poland attacked fellow students, teachers and passersby with a sharp object, wounding nine people. He was arrested nearby. 

The following day, a 15-year-old killed a school custodian and wounded two others in a knife attack at his former school in the same province.

The assaults, both carried out by Polish nationals, shocked a country where school violence is a new phenomenon. Police say there is no evidence the attacks were coordinated.