The attacks suggested that even as the military coalition's focus shifts to managing the drawdown, the United States appears likely to face an intense "fighting season," the springtime period in Afghanistan during which violence typically increases.
The American diplomat killed Saturday was a young officer who was recently tasked with supporting a trip to Kabul by Secretary of State John F. Kerry, the State Department announced.
Four other State Department officials who were with her, traveling to a school in the southern province of Zabul, were injured in the same bombing, one critically, Kerry said in a statement.
"She was everything a Foreign Service Officer should be: smart, capable, eager to serve, and deeply committed to our country and the difference she was making for the Afghan people," Kerry said. "She tragically gave her young life working to give young Afghans the opportunity to have a better future."
The attacks came as Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, arrived in Afghanistan to take stock of the war as U.S. officials continue to deliberate how quickly they should pull out the 68,000 American troops still deployed in the country.
Saturday's violence followed a coordinated attack Wednesday on a courthouse in the country's relatively safe west that killed at least 46 people. The Taliban claimed responsibility for the assault in Farah province, saying it had been carried out to avenge the group's fighters who have been "kept in prisons for years on end and even mercilessly given the death penalty."
In the deadlier of the two attacks Saturday, in Zabul province's Qalat district, insurgents detonated a bomb when a convoy transporting U.S. troops and State Department officials and another one carrying the governor of the province intersected. The blast, in an area that has long been a Taliban stronghold, killed three U.S. service members, the young diplomat and a U.S. Defense Department employee.
The Associated Press reported that an Afghan doctor was also killed in the explosion.
In a statement, the Taliban said the attack was carried out at noon when a militant detonated explosives packed in a vehicle as the provincial governor was approaching the Americans. A Taliban spokesman told the AP that militants linked to the group were hoping to strike a U.S. or an Afghan government convoy when they placed the bomb.
"We were waiting for one of them," spokesman Qari Yousef Ahmadi said. "It was our good luck that both appeared at the same time."
In the east, meanwhile, a third American civilian was killed in an "insurgent attack," according to a statement issued by the military coalition in Kabul. It offered no further details.
Dempsey, the country's top U.S. military official, told reporters traveling with him that he was heartened by what U.S. officials have described as spontaneous rebellions against the Taliban that have unfolded in recent months as the U.S. presence in the country has thinned.
He expressed hope that a political solution will lead at least some segments of the Taliban to join the political process, according to remarks published by the American Forces Press Service, a Pentagon news division.
"Any conflict in history, when it is resolved, is resolved through some form of reconciliation," Dempsey said. "I support the effort to try . . . through the Afghans to encourage them to take reconciliation as an important line of effort."
The State Department said the slain diplomat's family had been notified on Saturday, but officials did not immediately release her name, saying they wanted to give the officer's parents a chance to tell loved ones before the news broke. Kerry, who traveled Saturday to the Middle East, spoke to the woman's parents to offer "what little comfort I can for their immeasurable loss."
"As the father of two daughters, I can't imagine what their family is feeling today," he said.
