Three pickup trucks full of gunmen launched an attack on the main police station in Kunduz province's Aliabad district on Saturday afternoon, said Deputy Provincial Police Chief Abdul Rahman Aqtash.

"They started a gunbattle that lasted for about one and half hours," Aqtash said, with both police reinforcements and NATO air support called in.

One police officer was killed in the fighting, he said.

NATO said in a statement no one was killed or injured in the gunfight. It was not immediately possible to reconcile the discrepancy.

A NATO air team tracked the insurgents as they drove away, and fired on the truck after determining there were no civilians nearby, the statement said. Several other militants were wounded. Aqtash said the number killed may have been higher, but he was still confirming figures.

In the east, meanwhile, a crowd of protesters set upon US troops outside of Bagram Air Field - the main US base in the country. A number of people were wounded as the demonstration in Pul-e-Sayad village turned into a riot, NATO said.

The crowd of about 250 people gathered around the American troops to protest the building of an Afghan Army base on land owned by local villagers, said Abdullah Adil, an Interior Ministry official who works with NATO forces in the area. A few villagers had first gone to the construction site in the morning to demand that work be stopped and when it wasn't, they returned with a crowd of people, he said.

Protesters threw baseball-size rocks at the troops as they escorted a contractor to the base, NATO said.

The rocks injured some service members and when they couldn't quell the riot, a soldier fired at the crowd in self-defense, NATO said.

Three Afghans were wounded in the melee, NATO said, without saying who was at fault for the injuries. The troops offered to help the wounded, but the locals rejected the assistance, a statement said.

One 12-year-old boy was shot, but his wounds were not life-threatening, Adil said.

Construction has now been halted pending more discussion with the villagers, he added.

"The land dispute is clearly an Afghan government issue that must be settled in order to resolve the ongoing concern of Afghans from the village," Col. William F. Roy said in the NATO statement.