KABUL, Afghanistan — Three NATO soldiers and an Afghan civilian were killed Wednesday in a suicide attack in the middle of the provincial capital of Kunar Province in eastern Afghanistan.

The attack, in which two bombers detonated suicide vests as soldiers were patrolling near the provincial council’s office, occurred just a few days after the Taliban made a show of force in Kunar, a rugged border province that has been one of the most hard-fought regions for the American military. In those attacks, insurgents assaulted outposts and government buildings in eight districts, although few casualties were reported.

The transition of Kunar’s security to Afghan control is happening more gradually than in some other provinces, and the nature of the recent attacks shows why, in part: despite years of intensive coalition military offensives in some parts of the region, militants pose a perpetual threat, even in the provincial capital, Asadabad. The tenor and pace of attacks speak to the Taliban’s long-range strategy, in which civilians are regularly reminded of the militants’ resilience in a place where government control has always seemed tenuous.

Bolstering the sense of a tenacious insurgency was a report on civilian casualties released by the United Nations office here in Kabul. Despite a 15 percent drop in those casualties between Jan. 1 and June 30 of this year compared with the year before, officials emphasized that the improvements were being eroded.