At least six people have been killed after a bomb blast struck a marketplace in northwestern Pakistan, officials say.

The explosion on Friday morning also injured up to 20 others in the town of Kuki Khel in Khyber, a tribal region which sits along the border with Afghanistan.

"It is a remote area and what we got is it was bomb blast in which six people have been killed," Tariq Hayat Khan, a local security chief, said.

Shafeerullah Khan, a local administrator, said: "We are trying to ascertain nature of the blast."

Pakistan's military has recently launched several operations to drive out Taliban fighters and other groups from the mountainous region.

Khyber's security is also of paramount importance to the US because it is home to a major supply route for foreign troops in Afghanistan.

In recent weeks, there have been several major suicide bomb attacks in Pakistan.

On Thursday, a blast killed at least five people in the Swat valley, which is also in Pakistan's northwest.

Last week, a pair of suicide bombers blew themselves up in the Mohmand tribal region, killing at least 102 people in the deadliest attack in the US-allied country this year.

The attacks come as Washington is pushing Pakistan to do even more to root out armed groups that use its soil to plan attacks in Afghanistan.