Border Police General Abdul Raziq Khan said 11 others were wounded in the attack near Spin Boldak, a town on the Pakistani border.
Some reports say up to 10 people were killed in the blast. A NATO force soldier died in a separate bombing claimed by the Taliban in the southeastern province of Paktika.
Meanwhile, Afghan officials say a German national and his interpreter, who were kidnapped in Afghanistan's southwestern Nimroz Province on June 28, have been freed.
Interior Ministry spokesman Zemarai Bashary said the two were released today with the help of police.
"[The German's] health condition is very good," Bashary said. "He is healthy, safe, and they are currently with the police of Delaram district of Farah Province. There is no concern about their health and security. We are sure that he is safe, and now the police are taking care of them."
Earlier today the governor of neighboring Farah Province said that the kidnappers demanded a $40,000 ransom for his release. It's not clear if the ransom was paid to secure the men's release.
(AP, Reuters, AFP)