A prominent Pakistani journalist and anti-drone activist has gone missing after nearly two dozen men stormed his home and abducted him, his lawyer announced on Monday – just days before he was due to testify before European parliamentarians.

Kareem Khan was taken from his home in Rawalpindi – a city located just nine miles away from Islamabad in Punjab province – by approximately 20 men. Shahzad Akbar, Khan’s lawyer, told AFP that many of the men were wearing police uniforms, though the affiliation of the kidnappers remains unknown.

Khan was scheduled to depart Pakistan on Saturday to speak with German, Dutch, and British parliamentarians about his experience with drone strikes.

Khan originally hails from the tribal region of North Waziristan and became the first Pakistani man to sue the US government in connection with drone attacks that killed members of his family. Khan’s brother and son were killed in a strike in December 2009.

Akbar now maintains that Khan’s wife and children have not been given any information regarding his location, or why he was taken.

“We lodged a report with the local police but they denied having picked him up,” the attorney said. “It seems to be work of the intelligence agencies.”

Local police have denied any involvement, saying they have no record of a raid on the night in question.

Clare Algar, executive director at Reprieve – a legal charity based in the UK – wrote on the organization’s website that officials are growing concerned.

“We are very worried about Mr. Khan’s safety,” she wrote. “He is a crucial witness to the dangers of the CIA’s covert drone program, and has simply sought justice for the death of his son and brother through peaceful, legal routes. Reports that he was detained by men in police uniforms are of great concern, and we urge the Government of Pakistan to do everything in its power to secure his immediate release.”

He first filed suit in 2010, asserting that drone strikes murder innocent civilians and violate international law by subverting the international prohibition on assassinations away from a battlefield. Khan said he was not home at the time of the strike, but stated that neighbors witnessed a massive blast.

In addition to Khan’s brother and son, a construction worker also died in the strike. Khan’s brother was a teacher with a master’s degree in English, while his son was a staff member at a government school.

Senior US intelligence officials told CNN at the time that Khan was suspected of housing Haji Omar Khan, a notorious Taliban leader who was also killed in the strike. Khan has denied ever knowing Haji Omar Khan, who fought against the Soviet Red Army in Afghanistan before developing close ties with Mullah Omar.

Last year, Akbar – who represents a number of Pakistanis affected by drone strikes – and other activists published a letter in which they named the CIA station chief in Islamabad, accusing he and CIA director John Brennan of murder for their role in a drone strike late last year.

While exact figures are murky, AFP estimates that 2,155 Pakistanis have been killed in drone attacks since august 2008. It remains unknown how many of those killed were suspected militants and how many were civilians.