At least 18 people, including four women and eight children, were killed on Friday in Pakistan's restive tribal region along the border with Afghanistan when their houses were destroyed in explosions.

Islamist politicians immediately blamed American missile attacks from across neighbouring Afghanistan for the deaths.

A US spy plane fired missiles on the houses of three civilians at 0300 local time in Mamund locality of Bajur region, bordering Afghanistan's eastern Kunar province, a lawmaker belonging to the Islamist alliance Mutahida Majlis-e-Amal alleged.

Kunar is a restive Afghan province where Taliban militia and Hekmatyar-led Hizbe-e-Islami are active.

"A US spy plane had been flying in Bajur region for three days. The plane bombed three houses of locals in Damadola village, 50 kilometers from the Pakistan-Afghan border," said Sahibzada Haroon ur Rashid, Member National Assembly from Bajur tribal belt.

Apart from the 18 killed, four others, including two children, were injured and are stated to be in critical condition. Reports said one of the houses belonged to Gul Zaman, member of an outlawed Islamic extremist group.

Pakistan's military spokesman Major-General Shaukat Sultan and Information Minister Sheikh Rashid Ahmed have said the deaths occurred in an explosion and investigation is being carried out into the cause.