Protesters walked through Budapest’s frosty streets behind a banner reading “Protect the children!”, carrying soft toys and torches in solidarity with victims of physical abuse in a case dating back several years.

The prosecutor’s office said on Wednesday that seven people had been detained at the state-run Budapest juvenile centre so far.

Orban, who faces what could be the toughest challenge to his 15-year rule in an election likely in April, condemned the abuse in an interview with news outlet Mandiner, calling it unacceptable and criminal.

“More and more revolting things keep surfacing on a daily basis, which I did not think were possible in this country,” said Judit Voros, one of the protesters marching to Orban’s offices on Castle Hill in Budapest.

Earlier this week, the government placed Hungary’s five juvenile correctional institutions under direct police oversight while prosecutors investigate the case.

Prosecutors have been investigating the centre’s former director for months on suspicion of running a prostitution ring, money laundering and human trafficking.

A video published this week by opposition activist and former lawmaker Peter Juhasz prompted the resignation of the centre’s acting director.