Parliamentary candidate Habibullah Khan from the Garmser district of Helmand province, 600km south of Kabul, was severely wounded by a bomb placed at the door of his house early on Sunday, said district Police Chief Deljan.
"This was a mine planted for him in front of his gate by the enemies of peace and stability," he said, without blaming any specific group for the attack.
Similar attacks in the past have been blamed on the ousted Taliban.
In the southern province of Zabul, four Afghan policemen were killed in two separate attacks.
Three officers guarding a convoy transporting goods to US bases were killed when it came under fire from Taliban insurgents on Saturday.
The convoy was on its way from the provincial capital Qalat to US bases in Shinkay district 350km south of Kabul, said Shinkay's district governor Rozi Khan.
After the exchange of fire it turned back to Qalat.
Zabul, which shares a long mountainous border with Pakistan, is one of the provinces worst hit by the insurgency.
The Taliban has claimed
responsibility for recent killings
Taliban spokesman Abdul Latif Hakimi claimed responsibility for the attack in a telephone call from an undisclosed location.
Another policeman was killed in the neighbouring Shah Joy district of Zabul in a Taliban attack on the main highway linking the southern city of Kandahar with Kabul.
"One policeman was killed and two were wounded in a one-hour exchange of fire after the Taliban attacked a Kabul-Kandahar highway checkpost," Ghulam Nabi Mullah Khail, the highway police commander, said.
On Saturday, British citizen David Addison, who was captured by the Taliban on Wednesday, was found dead in the western province of Farah.
On the same day officials confirmed that two missing Japanese tourists had been shot and killed in the south.
Fighters from the Taliban ousted in late 2001 have stepped up attacks in a bloody countdown to parliamentary elections this month.
More than 1000 people, including hundreds of insurgents, have been killed this year.