German Chancellor Angela Merkel said Saturday for the first time that German troops were fighting a war in Afghanistan, as she addressed them on a surprise visit to the country, reporters with her said.

Her office said that she had arrived in Kunduz in northern Afghanistan to meet German troops serving there ahead of the Christmas celebrations.

She then went on to Mazar-i-Sharif for talks with Afghan President Hamid Karzai and the US commander of international forces fighting Taliban insurgents, General David Petraeus.

"What we have here is not just a warlike situation," she told the troops in Kunduz. "You are involved in combat as in war."

"This is a new experience," Merkel added on her third visit to Afghanistan while in office.

"We have heard such things from our parents talking of World War II, but that was different because Germany was the aggressor."

Thanking the troops for their service, she said, "We know that it's something very dangerous, and what you have experienced will weigh on many of you well after you return from operations."

Their mission in Afghanistan also served Germany, Merkel said. "Without it we couldn't live as peacefully, and people must know that. They sometimes view this operation with scepticism, but despite everything they are proud of you."

Merkel was accompanied by Defence Minister Karl-Theodor zu Guttenberg, who also visited Afghanistan last weekend with his wife to meet troops, and army chief General Volker Wieker.

Germany has 4,800 soldiers serving in the NATO-led International Security Assistance Force in Afghanistan, most of them in the north of the country, but their deployment is not popular at home.