Islamic militants ambushed a convoy of troops in Pakistan's troubled North Waziristan tribal area Wednesday, killing six soldiers and wounding at least 20 others in a hail of gunfire, the army said.

However, two intelligence officials, speaking on condition of anonymity because of the nature of their job, later put the number of soldiers killed at 13, saying seven of the wounded had subsequently died in a hospital.

Efforts to reach army spokesman Maj. Gen. Arshad Waheed for confirmation were not immediately successful.

Waheed said earlier that security forces backed by helicopter gunships spotted the fleeing militants and opened fire, killing 15 of them in "immediate retaliation."

Dozens of militants had targeted the convoy near the town of Dosali, 25 kilometers (15 miles) south of Miran Shah, the main town in the region.

Troops were searching for the remaining militants, Waheed said.

Earlier in the day, a roadside bomb exploded wounding six soldiers as another military convoy passed between the towns of Razmak and Mir Ali.

Waziristan borders Afghanistan and has been the site of a surge in Islamic militant activity in recent months.

Meanwhile, a lone motorcyclist shot and killed two police constables on a busy road in Quetta, said Rehmatullah Niazi, deputy inspector general of police in the capital of southwestern Baluchistan province. It was the third such attack in Quetta in less than a month, following the death of Baloch militant leader Balach Marri.