ISLAMABAD (AP) — Pakistan summoned a senior Afghan diplomat on Monday to lodge a formal complaint over a suicide attack in the country’s northwest, bordering Afghanistan, that killed 15 police officers.

Islamabad has blamed the late Saturday attack on the Pakistani Taliban, known as Tehrik-e-Taliban Pakistan, or TTP. Pakistani authorities have long accused the Taliban government of sheltering the TTP, a separate group but closely allied to the Afghan Taliban. Kabul denies the charge, saying it doesn’t allow militants to use Afghan soil to attack other countries.

The complaint was handed to the Afghan charge d’affaires, Pakistan’s Foreign Ministry said in a statement, adding that “a detailed investigation into the incident, along with evidence collected and technical intelligence” indicated that the attack was “masterminded by terrorists residing in Afghanistan.”

Kabul was also told that Islamabad “reserves the right to respond decisively against the perpetrators of this barbaric act,” the statement said.

There was no immediate comment from Kabul.

The attack in Bannu, a district in Khyber Pakhtunkhwa province, erupted after a suicide bomber, backed by several gunmen, detonated an explosives-laden vehicle near the security post, triggering a shootout. Some officers were killed in the exchange of fire, while others died after part of the building collapsed, according to local police. Four were also wounded.

A newly formed splinter group of the Pakistani Taliban, Ittehad-ul-Mujahideen Pakistan, claimed responsibility for the attack. Islamabad has accused the group of being a front for the Pakistani Taliban.

Also Monday, a suspected militant blew himself up prematurely, killing a civilian in a remote Jand village along the border with the northwestern Khyber Pakhtunkhwa, local police and authorities said.

The blast occurred after the civilian, Mohammad Liaquat, spotted the suspect walking from a farm field toward a nearby security post and questioned him because he was not recognized as a local resident. Local police official Mohammad Sabir said the attacker detonated his explosives in panic after being confronted in the small village, where residents know one another closely.

Interior Minister Mohsin Naqvi paid tribute to Liaquat, saying he saved many innocent lives by foiling the “nefarious designs” of the Pakistani Taliban. “Liaquat sacrificed his life to save others, and he is our hero,” Naqvi said in a statement.

Pakistan has witnessed a surge in militant violence in recent years, much of it blamed on the TTP.

Tensions between Islamabad and Kabul have persisted, with fighting that has killed hundreds of people since late February. In early April, Afghan Taliban and Pakistani officials held peace talks mediated by China. However, sporadic cross-border clashes have continued, though at a lower intensity than before.