At least eight people were killed and nine others wounded Thursday in two bomb blasts targeting minibuses in Kabul, according to police, in the latest attacks on commuters in the Afghan capital.

Two other buses were hit earlier this week, with fears rising that further unrest lies ahead as Washington withdraws its remaining troops in the coming months.

Police spokesman Ferdaws Faramarz said the first explosion happened on a road in southwestern Kabul near a neighbourhood largely populated by the Shiite Hazara community, who have been the frequent target of militant attacks.

Four people were killed in that blast, and four others wounded.

Hours later, a second bus was hit just a few kilometres (miles) away, Faramarz said, also in a Hazara neighbourhood.

No group has claimed responsibility for the attacks.

Earlier this week, the Islamic State group's Afghan affiliate claimed back-to-back attacks on two buses in Kabul that killed at least 10 people. 

Violence has soared in recent weeks as government forces and the Taliban clash in near-daily battles across the rugged countryside, with the militants appearing to focus on battering checkpoints and bases near Kabul.

The surge in violence comes as the US military continues to withdraw its remaining 2,500 troops from Afghanistan.

President Joe Biden has ordered the military to complete the pullout by the 20th anniversary of the September 11 attacks.

But as the Americans pack up, experts fear Afghanistan will remain home to a number of jihadist groups.

The United Nations Security Council warned in a report published Wednesday that IS continues "to pose a threat to both the country and the wider region", saying the group had approximately 2,000 fighters inside Afghanistan.