Pashtun Tahaffuz Movement (PTM) leader and MNA Mohsin Dawar was taken into custody on Tuesday in Islamabad, said Kohsar police Station House Officer (SHO) Akhtar Ali.
SHO Ali said that 15 workers of PTM, including Dawar, had been taken to Kohsar police station from outside the National Press Club in Islamabad, where they were demonstrating against the group's chief Manzoor Pashteen's arrest.
The total number of arrested demonstrators, however, can be higher as more protesters were taken to other police stations in Islamabad. A large number of supporters and PTM workers were attending the protest, including politicians Afrasiab Khattak and Bushra Gohar.
A journalist, Khan Zeb, was also among those arrested and was earlier misidentified by the police as PTM leader and MNA Ali Wazir, who was part of the protest.
SHO Ali later confirmed that Wazir had not been taken into custody and it was in fact the journalist, Khan Zeb, whom the police had believed to be Wazir. The journalist, the SHO told DawnNewsTV, would be released soon.
The development was also confirmed by Dawar.
"We are in police custody and [have been] shifted to Kohsar police station," he told DawnNewsTV via text message.
The reason for the arrests was not immediately clear. However, a police official, who spoke to DawnNewsTV on condition of anonymity, said that the protesters were arrested on the orders of higher authorities.
A video, shared by BBC correspondent Secunder Kermani on Twitter, purportedly showed the PTM leaders being arrested by the police.
Protests against the PTM chief's arrest were also held in various areas including Mir Ali, Tank, Miranshah and Zhob.
In Peshawar, PTM workers and supporters gathered outside the city's press club to protest Pashteen's arrest and demanded his immediate release.