Scores were killed when gunmen stormed a police training center in Quetta, Pakistan, late on Oct. 24. Most of the dead were police cadets, and another 117 people were seriously wounded. No group has claimed responsibility for the assault. (Video: Reuters / Photo: AP)

Gunmen in the southwestern Pakistani city of Quetta killed at least 61 people in a bloody assault on a police training camp, storming a dormitory of unarmed cadets in a shooting rampage before detonating explosive vests, government officials said Tuesday.

The assault — involving at least three attackers who also battled paramilitary forces — is the latest blow by militants operating along the lawless border with Afghanistan as Pakistan struggles to make gains against various insurgent factions.

It also was another direct strike at Pakistan’s powerful security forces. In September 2015, Taliban fighters stormed an air base in Peshawar, another border hub northeast of Quetta, killing at least 29 people.

The Islamic State claimed responsibility for the attack in a statement posted online Tuesday. The militants’ Amaq news agency published a photo of what it said were the three attackers, all operatives of the group’s so-called Khorasan Province faction, which is active in Afghanistan and Pakistan.

Pakistani troops enter the police training school that was attacked by militants in Quetta, Pakistan. (Arshad Butt/AP)

But a senior security official said Lashkar-e-Jhangvi, a Pakistani extremist group that has targeted the country’s Shiite Hazara minority over the years, was responsible for the bloodshed, which also left more than 100 people injured.

Hospital officials said at least 61 people were killed in the attack. Many of the wounded remained in critical condition, meaning the death toll could rise.

Two officials, including Maj. Gen. Sher Afgan, the chief of Pakistan’s paramilitary forces, said the militants had either crossed over from Afghanistan or were in contact with handlers on the Afghan side of the border.

Pakistani authorities have blamed Afghan militants for attacks inside Pakistan in recent years, despite Pakistan’s history of homegrown extremism.

Dozens of jihadist groups have emerged from the lawless border area between the two countries, and both sides are rife with militancy. Quetta, 150 miles from the southern Afghan city of Kandahar, has long served as a staging ground for insurgent activities in Afghanistan and is a base for leaders of the Afghan Taliban.

None of the officials gave any motive for the assault.

“First they tried to target the city, but due to a high security alert, they failed,” said Anwar ul-Haq Kakar, a spokesman for Baluchistan province, where Quetta is located.

“After that, they attacked the Police Training College,” he said. The college is less than 10 miles from central Quetta.

Security officials told local media that gunmen attacked a hostel inside the camp where cadets had retired for the night. Because the cadets were in training, they did not have their own weapons, one police official said. The official, speaking on the condition of anonymity, added that many of the cadets had completed their course and were preparing to return home.

Baluchistan’s home minister, Mir Sarfraz Bugti, told reporters that the gunmen killed a watchtower guard before slipping over the wall into the compound.

“I saw two gunmen firing as they ran toward us, toward our building,” a police cadet told Pakistan’s Geo News television channel. “We got to the roof and jumped down to save our lives.”

Footage aired on Pakistani television showed ambulances streaming out of the camp’s main gate. Firefighters also rushed to the scene.

Pakistani Prime Minister Nawaz Sharif, in a statement early Tuesday, directed authorities to bring the perpetrators to justice. U.S. State Department spokesman John Kirby also condemned the attack.

Monday’s attack was the latest in a string of deadly assaults in Quetta. In August, a suicide attack on a group of lawyers killed more than 70 people, including most of the province’s practicing attorneys. The Islamic State also claimed that attack, along with other groups.

The lawyers had gathered in the emergency room of a local hospital to view the body of a slain colleague. The attacker detonated an explosive vest in the middle of the crowd.

Cunningham reported from Kabul. Aamir Iqbal in Peshawar, Pakistan, and Brian Murphy in Washington contributed to this report.