Polish police said Saturday they detained about 50 demonstrators who tried to prevent the arrest of a gay rights activist in the capital Warsaw, which sparked criticism from rights groups.

The activist, who was referred to officially in court as Michal Sz. but who identifies as a woman named Margot, is suspected of causing damage to a van plastered with homophobic slogans in Warsaw in June.

A court order mandated two months of pre-trial detention for the activist, who is also accused of pushing a volunteer from the Pro-Right to Life Foundation which owned the van.

Margot was detained on Friday at the offices of Campaign Against Homophobia but dozens of protesters then blocked the police car, prompting a stand-off before officers cleared the way to allow it to pass.

Warsaw police said  48 people were arrested during the protest
Warsaw police said 48 people were arrested during the protest AFP / JANEK SKARZYNSKI

Warsaw police said on Twitter that 48 people were arrested in connection with "insults directed at police as well as damage to a police car."

"As soon as the man was arrested and taken into the police car, a group of people leapt toward the police car and started to jump on it," Warsaw police spokesman Sylwester Marczak said.

"We took steps to ensure both the safety of the police, the detainee and the safety of" a church which was the "target" of some of the protesters, he said.

Margot called pre-trial detention, which is normally used to prevent another crime being committed, a "repressive" measures, in comments to the PAP news agency before her arrest.

Police said some of those arrested had tried to block a police car transporting detained gay rights activist Margo
Police said some of those arrested had tried to block a police car transporting detained gay rights activist Margo AFP / JANEK SKARZYNSKI

Her arrest prompted outrage from opposition politicians and rights groups.

The Council of Europe's Human Rights Commissioner Dunja Mijatovic quickly called for Margot's release.

Mijatovic tweeted that the activist was detained "for blocking an anti-LGBT hate van and putting rainbow flags on Warsaw monuments," adding that an order for Margot's two-month detention sends a "very chilling signal" for freedom of speech and LGBT rights in Poland.

Margot belongs to a campaign group called Stop The Nonsense, which is also suspected of draping several Warsaw monuments, including a statue of Jesus Christ, with LGBT flags last week.

Prosecutors have charged three people in that case for desecrating monuments and hurting religious feelings.

Hanna-Gill Piatek, a leftist lawmaker, was at the scene of Margot's arrest.

"I wish serious criminals were prosecuted as diligently as activists," she said.

The van from the Pro-Right to Life Foundation is a common sight in the centre of Warsaw, blasting homophobic slogans and plastered with posters linking homosexuality to paedophilia.