Six American troops and civilians and an Afghan doctor were killed in attacks on Saturday in southern and eastern Afghanistan as the U.S. military's top officer began a weekend visit to the country, officials said.

In the south, three U.S. service members, two U.S. civilians and the doctor were killed when a suicide bomber detonated a car full of explosives just as a convoy with the international military coalition drove past another convoy of vehicles carrying the governor of Zabul province.

Another American civilian was killed in an insurgent attack in eastern Afghanistan, the U.S. military said in a statement.

The attacks occurred the same day that U.S. Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, arrived in Afghanistan for a visit aimed at assessing the level of training that American troops can provide to Afghan security forces after international combat forces complete their withdrawal at the end of 2014.

Those killed in Zabul province included three members of the military and two U.S. civilians, including at least one employee with the U.S. State Department, said a U.S. official who spoke on condition of anonymity ahead of a formal announcement. Several other Americans and Afghans, possibly as many as nine, were wounded, the official said.

The U.S. Embassy in Kabul confirmed that Americans were involved in an attack in Qalat, the capital of Zabul province. Zabul is next to Kandahar, the birthplace of the Taliban, and shares a volatile border with Pakistan.

"There are American and Afghan casualties. We are still investigating the incident and cannot confirm details at this time," the embassy said in a statement.

There were no immediate claims of responsibility for the attacks.

The deaths bring the number of foreign military forces killed this year to 30, including 22 Americans. A total of six foreign civilians have died in Afghanistan so far this year, according to an Associated Press count.

It was unclear if the car bomber was targeting the coalition convoy or that of Provincial Gov. Mohammad Ashraf Nasery, who was driving to an event at a nearby school in Qalat. The explosion occurred in front of a hospital.

Nasery, who survived the attack, said the car bomb exploded as his convoy was passing the hospital. He said a doctor was killed, and two of his bodyguards and a student from the school were wounded. The coalition convoy was leaving a base that is home to a provincial reconstruction team, or PRT, officials said.

"The governor's convoy was at the gate of the school," provincial police chief Gen. Ghulam Sakhi Rooghlawanay said. "At the same time the (coalition) convoy came out from the PRT and was passing by that place. The suicide bomber blew himself up between the two convoys."

Nasery said he thought his convoy was the intended target.

"I'm safe and healthy," he told The Associated Press in a telephone call. "The target was my vehicle, but I survived."