A roadside bomb has struck tribal police assigned to guard polio workers in northwest Pakistan, killing at least 12 people, police said.

Eleven soldiers and one child were reportedly among those killed in Saturday's attack in the Jamrod area in the northwest Khyber tribal agency of Pakistan. At least ten others were injured.

Elsewhere, a separate bomb blast killed at least three paramilitary soldiers and wounded six others in Balochistan, officials said.

The roadside bomb hit a patrol vehicle around 200km south of Quetta on a main road linking Balochistan to the port city of Karachi, AFP news agency reported.

"At least three soldiers were martyred and six others were wounded, when a bomb planted by miscreants exploded on the national highway," Frontier Corps spokesman Abdul Wasay said.

No group immediately claimed the responsibility for either of the attacks.

'Pipelines targeted'

In a separate development, Pakistani security forces killed six fighters in a separate exchange of gunfire in the Dera Bugti area in the country's southwestern Balochistan province.

An army spokesman told Al Jazeera on Saturday that the fighters were planning to blow up gas pipelines in the restive area.

Attacks on pipelines and railroad tracks have been on the rise in recent months, and Baloch separatists have before claimed responsibility for attacks on passenger trains.

Balochistan, which borders Iran and Afghanistan, is rife with separatist and armed groups and plagued by sectarian bloodshed.

Pakistani officials refer to Baloch fighters, who have been waging a bloody low-level separatist struggle for a decade, as "miscreants".

Source: Al Jazeera and agencies