In a statement, the Afghan foreign ministry called on German authorities "to investigate the matter, bring the perpetrators to justice and ensure such actions are not repeated."

Germany's largest-selling paper, the mass-circulation Bild, published photographs on Wednesday and Thursday of German soldiers stationed in Afghanistan posing with a human skull. The pictures, dated from early 2003, showed the soldiers holding the skull, putting it on the hood of their vehicle and in one picture, a soldiers exposes himself next to it.

The scandal widened Thursday evening when Germany's RTL television network said it received images showing a German soldier kissing a skull balanced on his left bicep and another soldier posing with a skull on the hood of a jeep used by the NATO-led International Security Assistance Force (ISAF).

The Afghan trade minister, Amin Farhang, expressed the worry that the photos could lead to escalation of tensions in the region, similar to the protests around the globe the followed the publication in a Danish newspaper of caricatures of the Prophet Muhammad.

"It could result in something like accompanied the caricatures, even though the two things are not comparable," Farhang told the Friday edition of the Kölner Stadt-Anzeiger daily.

"Afghans are very sensitive," he added. "Naturally, terrorists are going to make propaganda of it."

As of Thursday, there were no reports of protests or unrest in Afghanistan in reaction to the photos.

Hurt the mission?

Many have worried that the scandal could make an already difficult mission in Afghanistan more difficult. The country is deeply conservative and a Taliban insurgency there has been gaining strength.

"There is the potential for the alleged conduct of a few soldiers to be misrepresented and distorted in a way that can have a damaging effect," ISAF spokesman Major Luke Knitting told AP in Afghanistan.

Germany has about 2,800 soldiers serving with the 30,000-strong peacekeeping force in Afghanistan.

Despite the worries, the Afghan trade minister warned against over-dramatizing the situation, saying the incident involved only a small group and did not reflect the entire Bundeswehr, which he said had "honorably fulfilled its duty over the past few years."

Increased security

In reaction to the publication of the photos, the foreign ministry has increased security at some of its embassies throughout the Middle East.

"The embassies were told about the pictures early on so they could put the necessary security measures in place," a ministry speaker told reporters Thursday in Berlin.