Dad Mohammad Khan, a prominent Afghan politician, has been killed by a roadside bomb, Afghan officials say.

Four other Afghans died alongside Khan when a bomb blew up their vehicle on Thursday.

The group was travelling on the main road to Lashkar Gah, the capital of Afghanistan's southern Helmand province.

Khan, a member of the Afghan parliament, was a prominent critic of the Taliban, which lead the government from 1996 until 2001 when it was overthrown by a US-led invasion.

Shir Mohammad Akhonzada, the former governor of Helmand, said that Khan fled the country during Taliban rule but later returned as Helmand's intelligence chief.

Taliban fighters have maintained their armed struggle to regain power from the Western-backed administration.

No group has yet claimed responsibility for the attack. The government said the bomb was controlled remotely.