Gunmen stormed a police training centre in Pakistan's troubled Baluchistan province and detonated explosive vests, killing at least 48 trainees.
Baluchistan's senior health official, Noor Haq Baloch, said at least 116 people were wounded - mostly police trainees and some paramilitary troops.
One attacker was killed by security forces and two died when they detonated their explosive vests.
Major General Sher Afgan, chief of the paramilitary Frontier Corps, told reporters that the attackers appeared to be in contact with handlers in Afghanistan. He said they belonged to the banned Lashker-e-Jhangvi group, an Islamic militant group affiliated with al Qaida.
However, neither Lashker-a-Jhangvi nor any other group has claimed responsibility for the attack.
The Islamic State group and breakaway Taliban faction Jamaat-ul Ahrar have claimed responsibility for past attacks in Baluchistan - Lashker-e-Jhangvi has mainly targeted members of the minority Shiite sect of Muslims.
The attack started when between four and six gunmen opened fire as they rushed the hostel at the police training centre in a suburban area of the provincial capital of Quetta.
"They were rushing toward our building firing shots so we rushed for safety toward the roof and jumped down in the back to save our lives," one of the police trainees told Geo television.
The death toll was expected to climb, as many of the injured are in critical condition.
About 700 trainees were said to be at the base when it was attacked.