NATO troops have pulled out of the remote Korengal Valley in eastern Afghanistan, a strategic shift they say allows troops to focus their efforts on protecting higher population areas.

The joint commander of international forces in Afghanistan, Lieutenant General David Rodriguez, said in a statement Wednesday the move is part of the new U.S. counterinsurgency strategy aimed at driving insurgents from civilian centers.  He said troops would still be able to respond to crises in the valley if needed.

NATO troops have pulled out of other isolated outposts in eastern Afghanistan that have been used as Taliban bases.  

The Korengal Valley is considered especially perilous because its rugged and mountainous terrain is used by insurgents to attack troops, and smuggle weapons and fighters in from neighboring Pakistan.

Separately, Italian Foreign Minister Franco Frattini said Wednesday he was unhappy with the way Afghanistan was handling the arrest of three Italian aid workers accused of an assassination attempt against a local official.

Frattini told an Italian parliamentary hearing that Prime Minister Silvio Berlusconi had written to Afghan President Hamid Karzai demanding more information about the allegations.

The three workers with the charity Emergency were detained Saturday in southern Helmand province and accused of plotting to kill the provincial governor.

Also Wednesday, German Defense Minister Karl-Theodor zu Guttenberg made a surprise visit to the country, where he met with troops at the headquarters of Germany's contingent in northern Afghanistan.  His visit comes about two weeks after insurgents killed three German soldiers in an ambush.

Germany has more than 4,000 troops stationed in Afghanistan - the third largest foreign troop presence in the country after the United States and Britain.

A total of 39 Germans have been killed in Afghanistan since 2002.

A poll published on Wednesday in Stern magazine showed 62 percent of Germans want their troops to return home.

Some information for this report was provided by AP and AFP.