Pakistan police detained more than 12 people, including Afghan nationals, in connection with a suicide bombing that killed five Chinese engineers and their driver last week, a senior law enforcement source said Tuesday.

Beijing is Islamabad's closest regional ally and a key investor in Pakistan's faltering economy, but Chinese citizens have frequently been targeted by Islamist militants in recent years.

The engineers and their Pakistani driver were traveling towards the Dasu hydroelectric dam under construction by a Chinese firm in northwest Pakistan when a bomber rammed their vehicle and detonated.

"More than a dozen suspected individuals have been taken into custody," the police source told AFP on condition of anonymity. "Among the apprehended suspects are some Afghan nationals."

Islamabad has blamed a recent uptick in attacks in Pakistan on neighboring Afghanistan, accusing the Taliban government there of failing to rein in militants sympathetic to their cause.

The Taliban government in Kabul has repeatedly denied giving haven to militants.

However, the senior police source said "initial evidence suggests the involvement" of Pakistan's domestic chapter of the Taliban, which analysts say has close ties to the Afghan Taliban.

The group -- known as Tehreek-e-Taliban Pakistan (TTP) -- publicly denied involvement in the attack last Tuesday.

The bombing sparked a flurry of diplomatic activity from Islamabad, eager to protect the billion-dollar investments Beijing has pledged under its "Belt and Road" initiative.

Prime Minister Shehbaz Sharif visited Chinese workers at the Dasu construction site yesterday and said Pakistan "will not leave any stone unturned" to guarantee their safety.

"I will not rest until we have put in place the best possible security measures," he told workers.

"I can assure you that our strong hands will catch the culprits very soon."