BERLIN  Germany’s defense minister, Karl-Theodor zu Guttenberg, made a surprise visit to Afghanistan Friday amid a growing controversy over the killing of over 142 people, many of them civilians in a NATO airstrike last September.

Mr. Guttenberg, who is coming under increasing criticism from opposition parties here for failing to explain the circumstances behind the Sept. 4 4 airstrike, said he wanted to hear from German soldiers based in Kunduz, in northern Afghanistan, how the orders were given to call in NATO aircraft after two fuel tanker trucks had been hijacked by the Taliban. Mr. Guttenberg, who was appointed defense minister after elections in September , also intends to explain the government’s position, his ministry said in a statement released Friday.

The incident has already cost the jobs of senior military personnel. Last month, Mr. Guttenberg dismissed Germany’s top militaryofficer, Gen. Wolfgang Schneiderhan, and a state secretary in the Defense Ministry, Peter Wichert. He said they had withheld information about the number of casualties and how the attack was carried out. When more details emerged, Franz-Josef Jung, who was defense minister at the time, was forced to resign as labor minister because he too had withheld information about the number of casualties.

Initial Defense Ministry reports said about 30 people had been killed in the airstrike. They did not mention civilian casualties.