At least 18 Shia Muslims were killed on Tuesday after they were ordered off a bus in the northern district of Kohistan, the three experts said in a joint press release.
"These killings are extremely shocking and constitute acts that require the strongest response," said Rita Izs" the Independent Expert on minority issues. "They have sadly become a recurrent practice in Pakistan, and we urge the Pakistan Government to identify and prosecute the perpetrators and do everything possible to establish strengthened security measures."
The experts expressed their condolences to the families of those killed and to all the people of Pakistan who suffer from such acts of terror.
"These targeted killings once more display the appalling degree of religious hatred in a country where there seems to be a failure to protect the security of religious minorities," said Heiner Bielefeldt, the Special Rapporteur on freedom of religion or belief.
Christof Heyns, the Special Rapporteur on extrajudicial, summary or arbitrary executions, stressed that the Government has an obligation to take all necessary measures to protect the right to life. "Failure to take appropriate steps to prevent, investigate and punish for such acts is a violation of Article 6 of the International Covenant on Civil and Political Rights," he said.
The three welcomed the condemnation expressed by Pakistani Prime Minister Yousuf Raza Gilani.
"Such serious incidents demand, and communities have the right to expect, the most rigorous response possible from the Government," they said. They urged the Government to step up security in the face of the "clear and present threat faced by certain groups on the basis of their religion."
In a previous incident on 17 February more than 30 people were killed or wounded when a suicide bomber detonated an explosive close to a mosque in a mainly Shia neighbourhood in the Kurram tribal region.