Pakistani authorities should conduct an impartial probe into the murder of journalist and rights monitor Zaman Mehsud and bring the killers to justice, Human Rights Watch said on Thursday.
Gunmen fatally shot Mehsud on Wednesday while he was riding his motorbike in Tank in Pakistan's northwestern province of Khyber Pakhtunkhwa.
Taliban commander Qari Saifullah Saif claimed responsibility for the attack.
"We killed him because he was writing against us.... (W)e have some other journalists on our hit list in the region, soon we will target them," Saif told a western news agency.
Human Rights Watch said: "The Taliban's claim of responsibility for this latest killing of a journalist shows a cruel disregard for human life and free speech.
"Pakistan's government needs to move to bring the perpetrators of attacks on journalists to justice if these crimes are to stop."
Mehsud was a monitor for the non-governmental Human Rights Commission of Pakistan (HRCP) in South Waziristan.
The Tehreek-i-Taliban Pakistan, the Pakistani Taliban, may have killed Mehsud for his reporting on the armed conflict and human rights situation in South Waziristan, Human Rights Watch said.
The Human Rights Commission of Pakistan said on Mehsud's killing: "HRCP would also like to invite the attention of civil society and the government to the possibility that Mehsud and other activists might have been rendered more vulnerable by the environment of suspicion the state agencies have been creating with respect to civil society organizations and by attributing to them various anti-state activities."
The attack occurred a day after the International Day to End Impunity for Crimes Against Journalists.
Pakistan remains one of the most dangerous countries in the world for journalists, the rights group said in a statement.
More than 35 journalists and media workers have been killed in Pakistan because of their work since 2010.
On the Committee to Protect Journalists' Global Impunity Index, Pakistan was ninth on the list of countries in which the most journalists were murdered without the attackers being prosecuted.
Pakistani journalists routinely face harassment, intimidation, assault, kidnapping, and arbitrary arrest and detention.
While militant groups have a long and well-documented history of killings of critics and independent voices, Pakistan security forces have also been implicated in attacks on journalists, including abduction, torture and killings.
On September 9, unidentified assailants gunned down Aftab Alam, a senior journalist, near his home in Karachi.
In April 2014, unidentified gunmen attacked Hamid Mir, one of Pakistan's most famous television presenters, also in Karachi.
Mir survived the attack and Jang/Geo - his employer and the country's largest media conglomerate - accused the director-general of the military's powerful Inter Service Intelligence (ISI) of involvement in the incident.
The proceedings of the judicial commission formed by the government to investigate the shooting remain opaque and no findings have been made public.
In January 2011, Wali Khan Babar, a 28-year-old reporter, was shot dead in Karachi.
While the trial court convicted those accused of killing Babar, at least five people associated with the investigation, including a witness, police informers, police officers and a prosecutor, have been murdered.
In 2011, Saleem Shahzad, a reporter for the Hong Kong-based Asia Times Online and for an Italian news agency, disappeared from central Islamabad. His body, bearing visible signs of torture, was found two days later.
The circumstances of the abduction raised concerns that the ISI was responsible. The commission of inquiry set up to investigate the killing failed to identify those responsible.
