KABUL, Afghanistan -- Afghanistan's Taliban authorities have "beaten and detained" an academic who voiced outrage on live television against their ban on women's university education, his aide said Friday.

A spokesman for UN Secretary General Antonio Guterres called for the immediate release of veteran journalism lecturer Ismail Mashal and denounced "backsliding" by the Taliban on issues of women.

Mashal caused a storm by tearing his degree certificates to shreds on TV in December, protesting the edict ending women's higher education.

In recent days, domestic channels showed Mashal carting books around Kabul and offering them to passersby.

"Mashal was mercilessly beaten and taken away in a very disrespectful manner by members of the Islamic Emirate," Mashal's aide Farid Ahmad Fazli told AFP, referring to the Taliban government.

A Taliban official confirmed the detention.

"Teacher Mashal had indulged in provocative actions against the system for some time," tweeted Abdul Haq Hammad, director at the Ministry of Information and Culture.

"The security agencies took him for investigation."

Mashal -- a lecturer for more than a decade at three Kabul universities -- was detained on Thursday despite having "committed no crime", Fazli said.

"He was giving free books to sisters (women) and men," he added. "He is still in detention and we don't know where he is being held."

Footage of Mashal destroying his certificates on private channel TOLOnews went viral on social media.

In deeply conservative and patriarchal Afghanistan it is rare to see a man protest in support of women but Mashal, who ran a coeducational institute, said he would stand up for women's rights.

"As a man and as a teacher, I was unable to do anything else for them, and I felt that my certificates had become useless. So, I tore them," he told AFP at the time.

"I'm raising my voice. I'm standing with my sisters... My protest will continue even if it costs my life."

A small group of male students also held a brief walkout protesting the ban.

A spokesman for UN Secretary General Antonio Guterres denounced the detention.

"It's a very concerning development," said UN spokesman Stephane Dujarric. "The professor should be released immediately."

"This is just yet another sign of the backsliding, shall we say, that we're seeing in Afghanistan with the de facto authorities especially on issues of education for women and girls."

The Taliban promised a softer regime when they returned to power in August 2021 but they have instead imposed harsh restrictions on women -- effectively squeezing them out of public life.

In December, the authorities ordered all aid groups to stop their women employees coming to work. They have since granted an exemption to the health sector, allowing females to return to employment there.

Secondary schools for girls have also been closed for more than a year, while many women have lost jobs in government sectors.

They have also been barred from going to parks, gyms and public baths.