Afghan officials say a suicide bomber has blown himself up in the eastern province of Khost, killing at least four people.
Officials say at least two civilians and two intelligence agents were among those killed.
Khost's provincial police chief says he suspects the commander of a militia that has worked with U.S. forces was the target of the attack.
No one has claimed responsibility for the attack, although it was similar to other suicide bombings carried out by the Taliban.
Also Friday, provincial official Zalmai Ayoubi said at least 20 Taliban militants were killed after a clash with members of a U.S. security firm in southern Kandahar province.
Officials say the clash began when militants attacked a supply convoy of the private company, USPI, in Zhari district.
Aid agencies say at least 3,000 people have died in insurgency-related violence this year. The United Nations says more than 1,400 of those people were civilians.
International and Afghan forces have been fighting militants sympathetic to the Taliban and al-Qaida for the past seven years.
Some information for this report was provided by AFP and Reuters.