According to reports, he has been missing since Mar 2. A formal case has been filed with the Swedish police.

He was publishing an online magazine named Balochistan Times.

In the magazine, Hussain reported on alleged human rights abuses in Pakistan's restive Balochistan province, where he hails from. For more than a decade, political and armed groups in Pakistan's largest province in the southwest, home to more than 12 million people, have been waging a separatist movement, reported Al Jazeera.

His wife Shahnaz Baloch, who lives in Balochistan, told Al Jazeera they were in contact on the day he went missing.

"I don't know how he went missing or where he is right now. We need the Swedish police to help us locate my husband. They initially said that it was normal in Sweden for someone to go in isolation. We are concerned about his safety and wellbeing. It is very unusual for a journalist like Hussain to go somewhere without informing us," Shahnaz Baloch told the news channel.

Jenny Johansson, case officer at Missing People (Sverige), an NGO that works with the Swedish police to find missing people, told Al Jazeera the group was in regular contact with the police to find Hussain.

"We don't have a clue so far. We only know his last location and we are working from that angle in close collaboration with the police," she said. "Because of his background and his job, this case is pretty unique."

Erik Halkjaer, president of the Swedish chapter of Reporters Without Borders (RSF), urged Swedish police to continue to investigate Hussain's disappearance, which he also said could have been due to his work, reported Al Jazeera.

"At this point, we can't ignore the possibility that his disappearance might be work related," he said.

In an email to Al Jazeera, Daniel Bastard, the Asia Pacific head of RSF, said Hussain could be a victim of enforced disappearance, given the circumstances of his case and testimony by his family and colleagues.

"When you think about who could find interest in suppressing a dissident journalist, the first hypothesis leads to Pakistan's Inter-Services Intelligence," he said, referring to the country's main intelligence agency, the ISI.

"We also know that two other Pakistanis based in Europe have been the victims of pressure upon their family back home in the past two months. And we know that a list of possible targets among Pakistan dissidents abroad is circulating," said Bastard.

"The fact that Sajid Hussain was writing about human rights and the situation in restive Balochistan makes him a potential priority target."

Central Information & Cultral Secretary of Baloch National Movement Murad Baloch said he is deeply concerned over the missing of the journalist.

"I am deeply concerned about disappearance of Sajid Hussain in Sweden who is a senior journalist & Chief Editor of @BaluchistanTime The Sweden government must fulfill their significant role for his immediate recovery. SwedenUN @dagensnyheter," he tweeted.

Murad Baloch, the Secretary-General of the Baloch National Movement, further expressed his doubt that Pakistan's spy agencyInter-Service Intelligence (ISI) might be behind the 'abduction' of the journalist.

"Sajid Hussain besides belonging to a political family is a renowned journalist. He has played a vital role in showing the true face of humanitarian crisis in Balochistan in front of the world. He has been writing in both Balochi and English languages on his online newspaper Balochistan Times," he was quoted as saying by The Balochistan Post.

"Furthermore, Balochistan Times also broadcasts a radio channel to give a voice to the voiceless Balochistan. His mysterious disappearance extremely shocked us and we have a concern that Inter-Service Intelligence (ISI) is behind his abduction," he said.