Police in Pakistan said Wednesday that a roadside bomb blast near the border with Afghanistan tore through a vehicle, killing a former senator and his four companions.

Initial police investigations concluded that suspected militants used a remote-controlled device to detonate an improvised explosive device in the troubled Bajaur district, noting that it was aimed specifically at the slain former member of the upper house of parliament, Hidayatullah Khan.

No group immediately took responsibility for the deadly bombing.

Militants affiliated with outlawed Tehrik-i-Taliban Pakistan, or TTP, and a regional Islamic State affiliate, known as IS-Khorasan, routinely target security forces and pro-government tribal elders and politicians in Bajaur and surrounding districts of Khyber Pakhtunkhwa province.

The TTP denied involvement in Wednesday’s attack but reiterated that its violent campaign is targeting only Pakistani security forces and those working for them.

Anti-terror drill with US

The bombing in Bajaur occurred while military personnel from Pakistan and the United States were participating in a two-week-long joint counterterrorism exercise in another part of the turbulent province, located about 160 kilometers (100 miles) northwest of Islamabad.

The bilateral drill began on June 29 at the National Counter Terrorism Center in the town of Pabbi in Khyber Pakhtunkhwa, with infantry companies from both countries participating.

It is designed to “exchange tactical skills at combating the menace of terrorism at sub-unit level,” a Pakistani military media wing announcement said Wednesday.

“The exercise is aimed at sharing counter-terrorism experiences besides refining drill procedures vital for counter-terrorism operations,” the statement said.

Terrorist attacks have sharply surged in Pakistan, killing hundreds of civilians and security forces in recent months.

Pakistani military and police have stepped up counter-militancy operations in violence-hit parts of the country, killing scores of TTP and insurgents linked to other groups.

Islamabad accuses the ruling Taliban in Afghanistan of providing sanctuaries to TTP and even facilitating their cross-border attacks.

Taliban government spokesperson Zabihullah Mujahid reiterated Wednesday that they are not allowing anyone to use Afghan soil to threaten Pakistan or any other countries.

Mujahid said, while addressing a news conference in Kabul, that Pakistani authorities should stop pointing fingers at Afghanistan for what he described as their internal security problems.