At least nine people, including two off-duty military personnel, were killed when gunmen opened fire on a bus traveling through northern Pakistan, causing it to crash into an oncoming truck and catch fire, officials said Sunday.

The bus was attacked at around 6:30 p.m. local time (01.30 p.m. GMT) on Saturday from both sides by at least five militants.

"Following the firing, the bus lost control and collided with an oncoming truck. Subsequently, both vehicles caught fire. Among the casualties are both drivers," said Arif Ahmed Khan, a senior government official for the district.

He said eight people died at the scene while one person later died in hospital.

Two army troops who were taking leave were among those killed, while 25 others were wounded.

The attack happened near Chilas in Gilgit-Baltistan, along the Karakoram Highway that connects the capital Islamabad to the mountainous north and China, tracing one of the many paths of the ancient Silk Road.

The bus was traveling south to the garrison city of Rawalpindi, which neighbors the capital.

No group has claimed responsibility for the attack, but the region has long grappled with sectarian violence between Sunni and Shiite Muslims.

Chilas, a town within the popular tourist destination of Gilgit-Baltistan, lies close to the Diamer-Bhasha Dam, a Chinese-backed mega project being built on the River Indus.