Professor Faizullah Jalal was detained in Kabul on Saturday and taken to an unknown location by Taliban forces, who stormed back to power in August.

Since their takeover, the Taliban have cracked down on dissent, forcefully dispersing women's rights protests and briefly detaining several Afghan journalists.

"After more than four days of detention on baseless charges, I confirm that Professor Jalal is now finally released," tweeted his daughter Hasina Jalal, a fellow at Georgetown University in Washington, after launching a social media campaign calling for his release.

Government spokesman Zabihullah Mujahid had tweeted that Jalal had made statements on social media in which he was "trying to instigate people against the system".

"He has been arrested so that others don't make similar senseless comments... that harm the dignity of others," he added.

Jalal's family said the tweets shared by Mujahid were from a fake Twitter account they had tried to get shut down.

"The Taliban are just using these posts as an excuse to silence a strong voice within the country," Hasina told AFP after the arrest.

Clips of Jalal's television appearances attacking the Taliban's forceful rule and the worsening economic situation had previously gone viral on social media, sparking concern he risked Taliban retribution.

In one live talk show, he called Taliban spokesman Mohammad Naeem -- who was also participating -- a "calf", a grave insult in Afghanistan.

Jalal, in his late 50s, had refused offers to leave the country after the Taliban seized power, living mostly in hiding in Kabul while his family fled to Europe, his daughter said.

A long-time professor of law and political science at Kabul University, Jalal has earned a reputation as a critic of Afghanistan's leaders over the past decades.