The ministry blamed the attack on the "opposition," a reference to the Taliban and other fighters trying to destabilise the government.
Fighters continue to target the police, who are seen as weaker than the Afghan army and international troops stationed in the country.
In Khost province, located on the border with Pakistan, at least four people were killed, including a woman and child, when a remote-controlled bomb exploded underneath a pick-up truck, said Colonel Mohammad Yaqoub Mondozai, the deputy provincial police chief.
Mondozai also said that three other people were wounded.
In the capital Kabul, a suicide bomber blew himself up, wounding five people, the interior ministry said.
There was no claim of responsibility for the attack.