A high-profile civil rights activist has been arrested in Pakistan on charges of sedition in the latest incident in a mounting crackdown on critics of the army.

Manzoor Ahmad Pashteen was arrested in the north-western city of Peshawar at around 2am on Monday morning on five charges, including criminal conspiracy and sedition.

The 28-year-old is the charismatic leader of the Pashtun Tahafuz Movement (PTM), which defends the rights of of Pakistan’s largest ethnic minority, the Pashtuns.

He has established himself as a thorn in the side of the powerful military, publicly accusing it of human rights abuses including kidnappings and forced disappearances, and of secretly allying with the Pakistani Taliban. The PTM has also drawn thousands of people on to the streets in protests against the military over the past two years.

The civilian Pakistan government, led by the prime minister, Imran Khan, is notorious for its alleged close ties to the military. Since Khan’s election, journalists, activists and critics of the military have increasingly been targeted, silenced and detained.

In an interview with the Guardian hours before his arrest, Pashteen emphasised how the PTM was “non violent” and simply seeking “justice and the Pakistani courts to do their job”.

“The PTM has demanded the formation of a ‘truth commission’ to investigate extrajudicial killings, land mines in former federally administered tribal areas region and enforced disappearances,” he said over the phone as he drove to Peshawar. He was detained hours later.

Pashteen added: “We want fundamental rights ensured by Pakistani constitution. We are against human rights abuses and torture. Our movement is to provide justice to [the] Pashtun minority who have been affected due to the war against terror.”

The police’s first incident report (FIR), seen by the Guardian, stated that Pashteen was arrested on the basis of a speech made on 18 January, in which he called the Pakistan constitution “wrong” and “against human rights” because it enshrined the rule of the Punjabi majority and stripped the Pashtuns of power.

Pashteen will be held in pre-trial police detention for the next two weeks. Some of the charges he is facing carry life sentences.

Pashteen was born in the war torn region of Pakistan’s South Waziristan, formerly referred to as federally administered tribal areas (FATA), which borders Afghanistan and has been decimated by years of fighting between militants and government forces. Pashteen’s family was one of millions who fled the region during clashes between the Pakistani military and insurgents between 2004 and 2017.

He shot to fame as a civil rights activist in January 2018 when he and others in the Pashtun community began protests against the extrajudicial killing of a young man at the hands of the anti-terrorism police officer Rao Anwar in Karachi. Anwar also is accused of the extrajudicial deaths of 444 people.

Pashteen began the PTM two years ago but it quickly gathered momentum in its opposition to the military’s actions in the former FATA, despite an almost blanket media blackout on their activities. In turn, the authorities have increasingly targeted PMT members and activists and the military publicly accused the PMT of being funded by foreign intelligence services.

Sanna Ejaz, a female leader of the PTM, said: “Manzoor was arrested last night on false charges. We never have been anti-state nor anti-constitution. We demand constitutional rights.”

Ejaz described how members of PTM had been targeted and said she had lost her job as a TV host because of her involvement with PTM activism. “My family has been harassed, I am harassed,” she said. “As a female activist, our pictures get used in negative ways to threaten our families. The military establishment has developed a sense of fear by killing our activists and harassing them so that people don’t join PTM and ask for democratic rights.”

In May, two of senior PTM figures, Mohsin Dawar and Ali Wazir, were detained after a clash between PTM members and army personnel in North Waziristan, and held for four months on no charges.

In a Twitter post, Dawar condemned Pashteen’s arrest. “This is our punishment for demanding our rights in a peaceful democratic manner,” he said. “But Manzoor’s arrest will only strengthen our resolve.”