Scores of people, including tribal elders and religious leaders, have been killed by suspected fighters in recent years in the border region for alleged collusion with the Pakistani authorities or spying for the US.
A suicide bomber dressed in a doctor's coat has blown himself up at a hospital in Khost, wounding at least two Nato soldiers.
A spokeswoman for the Nato-led International Security Assistance Force (Isaf) said: "We are aware of a number of casualties and we are investigating."
The attacker struck as doctors were meeting staff from an Isaf-run provincial reconstruction team (PRT) and the provincial governor.
Mohammad Yaquob, a police colonel, said: "The attacker in a white doctor's coat tried to enter a room in the hospital where officials including the governor were meeting with PRT staff.
"An American soldier tried to stop him, but he refused and blew himself up. One soldier was wounded."
There was no claim of responsibility but a series of similar attacks around the country in the past nearly two years have been blamed on Taliban fighters.
There were nearly 140 such attacks last year up from 27 in 2005, according to US officials.
Afghan and international troops have retaken a district capital in southwestern Afghanistan, pushing out Taliban fighters who had held the town for about 24 hours.
The Afghan interior ministry said the town of Bakwa in the western province of Farah was under government control and security reinforcements were there.
Zemarai Bashary, a government spokesman, said: "We occupied Bakwa this morning at 0100 GMT and the Taliban were pushed back."
About 300 Taliban stormed the town on Monday, forcing out police who fled the area, provincial officials said.
Taliban fighters captured a handful of districts last year but were pushed out by international forces backing the fragile Afghan government.
However, they have been holding the southern town of Musa Qala, about 150km east of Bakwa, for more than two weeks.
The authorities say they are waiting for the right time to retake the area.
In a separate incident, a US soldier has been killed in fighting with Taliban forces in the eastern province of Kunar.