Pakistani militants have killed at least 41 people in two separate incidents today challenging assertions that military offensives have broken the back of hardline Islamist groups.

In the north, 21 men working for a government-backed paramilitary force were executed overnight after they were kidnapped last week.

Elsewhere, a suicide bomber driving a vehicle packed with explosives rammed into a bus carrying Shia Muslim pilgrims in southwest Pakistan, killing 20 people.

Over 24 people were injured in the attack today in Baluchistan province's Mastung district.

The blast completely destroyed the bus that was hit and damaged a second bus carrying Shias that was close by.

An eyewitness who was travelling in the second bus told Geo TV that the pilgrims were headed to neighbouring Iran.

Iran, a majority Shia country is a popular religious tourism destination.

Pakistan has experienced a spike in killings over the last year by radical Sunni Muslims targeting Shias who they consider heretics, especially in Baluchistan.