(CNN) -- Two attacks in Afghanistan killed six Americans -- four service members and two civilians -- on Saturday as a top U.S. military official arrived to assess the country's security, officials said.
The deadliest attack was the bombing of a military convoy delivering books to a school in southern Afghanistan's Zabul province in which three service members, a State Department civilian and a Department of Defense civilian were killed, according to U.S. officials.
Afghan civilians also died in that incident, said U.S. Secretary of State John Kerry. Four more State Department personnel suffered injuries, one of them critically, Kerry said.
Meanwhile, another U.S. service member was killed in a separate attack, a U.S. official said.
Kerry described the killed State Department civilian as "an exceptional young foreign service officer" whom he met last week in Kabul.
She was on her second tour in Afghanistan, and had been working out of the embassy in Kabul since last summer.
Information on the other killed Americans, including their identities, wasn't immediately available.
"I wish everyone in our country could see first-hand the devotion, loyalty and amazingly hard and hazardous work our diplomats do on the front lines in the world's most dangerous places," Kerry said in a statement. "Every day, we honor their courage and are grateful for their sacrifices, and today we do so with great sadness."
Meanwhile, U.S. Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey arrived at Bagram Airfield on Saturday for meetings with coalition and Afghan leaders, the Defense Department said.
Dempsey will be apprised of an ongoing military transition where Afghan security forces are taking greater control of their country.
He will meet with Marine Corps Gen. Joseph F. Dunford, who took command of NATO's International Security Assistance Force (ISAF) about two months ago.
"One of the things I'm going to ask [Dunford], is ... what have you learned. If he tells me 'Nothing,' I'm going to say, 'Maybe we got the wrong guy,'" Dempsey told the American Forces Press Service.
Dempsey spokesman Col David Lapan later told CNN that Gen Dempsey was simply joking when he made the remark about Dunford.. Lapan said Dempsey has total confidence in Dunford.
Dempsey's other meetings will be with Army Gen. Lloyd Austin, commander of U.S. Central Command; U.S. Ambassador to Afghanistan James B. Cunningham; and Dempsey's Afghan counterpart, Army Gen. Sher Mohammad Karimi, the Defense Department said.
CNN's Jill Dougherty, Jamie Crawford, Chris Lawrence and Barbara Starr contributed to this report.