Family and friends said Anne Smedinghoff had chafed at the restrictions that American diplomats can face in Afghanistan, where the excitement and passion for foreign service are often dampened by lives circumscribed by blast walls and checkpoints and fortified compounds.

Ms. Smedinghoff joined the Foreign Service three years ago, straight out of Johns Hopkins University, and moved to Kabul in July. Being locked in the embassy compound, though it kept her largely safe from suicide bombers and rocket attacks, was not for her, her family and friends said. She longed to be out among Afghans, helping to ease the tumult of their lives.

On Saturday, Ms. Smedinghoff, 25, got her chance. She joined a delegation accompanying the governor of Zabul Province to inaugurate a new school in Qalat, the provincial capital. She was to help deliver donated books.

At 11 a.m., a suicide car bomber detonated explosives that ripped into the convoy, killing Ms. Smedinghoff and four other Americans — a civilian and three soldiers — in the deadliest day for Americans in Afghanistan this year. The names of the other four victims had not been released Sunday night.