A suicide bomber killed 21 people, including three US soldiers, in an attack on a joint Nato-Afghan military checkpoint in a province of Khost,on Wednesday . Another 37 people were wounded in the blast hospital officials said.
It is the second major attack on Nato this month in the town, and third in a row, after a suicide truck bomber targeted a US-run base on June 1 in an incident that killed up to 15 people.
Eleven bodies were brought to Khost's main hospital, said hospital director Majid Mangal. He said those included a police officer and a 15-year-old. Another six bodies were brought to the private Badari Clinic in Khost, said Mohammad Ayub Jan, a doctor at the clinic.
On Monday, three gunmen dressed in Afghan police uniforms killed one American service member and wounded nine others in Kandahar's Zhari district.
On Tuesday, Taliban suicide attackers struck two Afghan-Nato facilities in the southern province of Kandahar - the birthplace of the extremist movement and the heartland of its insurgency.
South-east Afghanistan's border provinces are a base for the al-Qaeda-linked Haqqani group, which frequently targets US and Afghan troops using suicide bombers.
There was no immediate claim of responsibility but the government blamed "enemies of Afghanistan", a phrase commonly used by officials to refer to the Taliban.
For the past five years the number of civilians killed in the war has risen steadily, reaching a record 3,021 in 2011 – the vast majority caused by insurgents, according to UN figures.
The US-led Nato force is also responsible for hundreds of civilian casualties every year, mostly in air strikes aimed at insurgents in Afghan villages.