Islamabad: At least six persons were killed and four others injured when a bomb hidden in a donkey cart exploded in a market in northwest Pakistan's tribal belt on Sunday, officials said.

The donkey cart with sand was left in the market of Mastak town in Khyber tribal region. An explosive device hidden in the sand was detonated by remote control, the officials said.

The blast killed six persons instantly, they said. The four injured people were out of danger.

No group claimed responsibility for the bombing though such attacks are usually blamed on the local Taliban and other militant groups like the Lashkar-e-Islam that are active in Khyber tribal agency.

At least 12 people were killed in two militant attacks in Khyber on Saturday.

Six militants were killed when troops repulsed an attack on a security check post in Malik Deen area. Six persons -- four children and two women -- were killed when a mortar fired by militants hit a house in Spah Darri area.

Pakistan army has conducted several operations targeting the Lashkar-e-Islam in Khyber but militants continue to be active in the region.