ISLAMABAD (Reuters) - A Pakistani activist affiliated with a group that has angered the country’s powerful military with its campaign against disappearances was arrested on Monday, an MP said, leading Amnesty International to call for him to be charged or immediately released.

Alamzeb Mehsud was picked up by police and security officials in plain clothes in the southern metropolis Karachi, said parliamentarian Mohsin Dawar, causing a social media outcry fearing that he was the latest activist to go missing in the South Asian nation.

Karachi police did not respond to requests for comment on the matter.

Mehsud is a founding member of the Pashtun Tahaffuz Movement (PTM) that has called for answers to the thousands of unresolved missing persons cases in Pakistan, primarily from the ethnic Pashtun region bordering Afghanistan.

PTM leaders hold Pakistan’s army responsible for the scores of disappearances that have taken place during military operations against Taliban militants in the region.

The army has said it does not detain individuals without evidence.

“There was a lot of social media outcry and after that the police said he was in their custody and filed a (first information report),” Dawar, who is also a prominent PTM leader, told Reuters.

Soon after Mehsud’s disappearance, Amnesty International put out a statement on Twitter calling for him to be produced in court or immediately released.

“We are concerned about reports of the disappearance of PTM activist Alamzeb Mehsud. His whereabouts must be disclosed immediately. Either produce him in court or release him without delay,” Amnesty said.

“Other PTM activists with him were allegedly beaten up. Freedom of peaceful assembly must be protected,” Amnesty said.

Dozens of PTM workers have been detained in the past few months in an ongoing crackdown against the group that began soon after it emerged in January last year.

“People are picked up, interrogated, and then released,” Dawar said.

PTM rose to prominence following the killing of a young Pashtun man in Karachi by police officials.

Its protests against alleged extrajudicial killings, arbitrary detention and “disappearances” of young Pashtun men have drawn widespread support across the country.

Last year, in the lead up to a PTM rally in Karachi, more than 100 PTM workers were detained an interrogated by the paramilitary rangers.

In December, Dawar and fellow PTM leader Ali Wazir, who were both elected to parliament from Pakistan’s Waziristan region that borders Afghanistan, were placed on the no fly list after cases against them were filed for their criticism of the military at PTM rallies. Their names have since been removed from the list.