The United Nations has demanded the Taliban provide information on two more women activists allegedly detained by the group this week -- bringing to four the number missing in Afghanistan this year.

Since their August return to power, the Taliban have cracked down on dissent by forcefully dispersing women's rallies, detaining critics and beating local journalists covering protests.

The United Nations Assistance Mission in Afghanistan (UNAMA) said late Thursday it had sought "urgent information" on the reported detention of two more women activists by the Taliban in the capital Kabul this week.

"UN repeats its call for all 'disappeared' women activists & relatives to be released," it said on Twitter.

US special envoy to Afghanistan Rina Amiri also called on the Taliban to respect women's rights.

"If the Taliban seek legitimacy from the Afghan people & the world, they must respect Afghans' human rights -- especially for women," she said on Twitter.

UNAMA did not reveal the names of the two women activists gone missing this week, but another rights advocate told AFP that Zahra Mohammadi and Mursal Ayar had been arrested by the Taliban.

"Zahra, a dentist, used to work in a clinic. She has been arrested," the activist said, on condition of anonymity.

Ayar was arrested on Wednesday after a male colleague asked for her address so he could come to hand over her salary, the activist said.

"That's how she was trapped. The Taliban found her and arrested her," she said.

She said Ayar's father had also been arrested, after mistakenly identifying Mohammadi's father as the man detained in an earlier interview.

The latest detentions come less than a month after activists Tamana Zaryabi Paryani and Parwana Ibrahimkhel went missing after participating in a Kabul protest.

The UN High Commissioner for Human Rights has expressed concern for the two women and four of their relatives, who all remain missing.

The Taliban have denied any knowledge of their whereabouts and say they are investigating the matter.

The hardline Islamists have promised a softer version of the harsh rule that characterised their first stint in power from 1996 to 2001.

But the new regime has been swift to bar women from most government jobs and close most girls' secondary schools.