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.
A protest was also held outside the Karachi Press Club and was attended by PTM supporters and members of civil society.
The PTM chief was arrested on Monday from Peshawar's Shaheen Town and was sent to the city's central jail on a 14-day judicial remand. Earlier today, he was shifted to Dera Ismail Khan on the orders of a local court.
According to police, a case was registered against the PTM chief at the City Police Station in DI Khan on January 18 under sections 506 (punishment for criminal intimidation), 153-A (promoting enmity between different groups), 120-B (punishment of criminal conspiracy), 124 (sedition), and 123-A (condemning the creation of the country and advocating the abolishment of its sovereignty) of the Pakistan Penal Code.
According to the first information report, a copy of which is available with Dawn.com, Pashteen and other PTM leaders had attended a gathering on January 18 in DI Khan where the PTM chief had allegedly said that the 1973 Constitution violated basic human rights. The FIR added that Pashteen also made derogatory remarks about the state.
Police had also arrested nine other PTM workers who were identified as Muhammad Salam, Abdul Hameed, Idrees, Bilal, Mohib, Sajjadul Hassan, Aimal, Farooq and Muhammad Salman.
PTM is a rights-based alliance that, besides calling for the de-mining of the former tribal areas and greater freedom of movement in the latter, has insisted on an end to the practices of extrajudicial killings, enforced disappearances and unlawful detentions, and for their practitioners to be held to account within a truth and reconciliation framework.
The party has been critical of the state's policies in the country's tribal belt, where a massive operation against terrorists was conducted in recent times leading to large-scale displacement and enforced disappearances.
PTM's leaders, in particular its elected members to the National Assembly, have come under fire for pursuing the release of individuals detained by authorities without due process. The army alleges the party of running an anti-national agenda and for playing into the hands of the state's enemies.
This is the second time Dawar has been arrested by police during a public gathering. Last year, he and Wazir were arrested after a protest gathering in Kharqamar for allegedly using violence and clashing with army personnel. The party while rejecting these allegations, insisted that theirs is a peaceful struggle for the rights of people from the country's tribal belt.