A suicide bomber has blown himself up in the Afghan capital of Kabul, quickly followed by a car bomb nearby in what appears to be have been a coordinated operation, authorities said.

At least 21 people had died and 45 more wounded were taken to hospital after Tuesday's attacks, public health ministry spokesperson Ismail Kawasi said. Initial eyewitness estimates pointed to around 50 casualties.

The attacks occurred at rush hour in an busy area home to government and legal offices, and were immediately claimed by the Taliban, who apparently targeted a minibus carrying Afghan intelligence agency staff and members of parliament.

The incidents come after a period of relative calm in Afghanistan's capital despite the years of Taliban insurgency aimed at overthrowing the government and removing foreign soldiers from Afghan soil.

Earlier on Tuesday, Lashkar Gar in southern Helmand province was also hit by a suicide bomber in an attack that killed seven people.

The assailant had targeted a guesthouse used by a local intelligence officer, and both military personnel and civilians were among the dead, the local police chief said.