An unidentified US World War I soldier whose remains were accidentally uncovered in northern France last year was buried with full military honours today, in the first such ceremony for 35 years.

Hundreds of thousands of troops - many undiscovered or unidentified - are buried across northern France, the epicentre of brutal trench warfare that defined the 1914-1918 conflict's western European front.

The unknown US soldier is believed to have been killed in July 1918 and was identified as American by equipment found alongside a few bones that were the only remains of his body.

He was buried today at the Oise-Aisne American Cemetery, around 113 kilometres northeast of Paris, which holds the graves of more than 6,000 other US soldiers killed in a 1918 offensive against German forces.

French, US and German army units attended the ceremony, during which the soldier was awarded a medal by American army chief of staff James McConville.

The cemetery's superintendent Hubert Caloud said it was the first time since 1988 that a US serviceman had been buried at an American World War I battle commission monument in France.

"For 105 years, this guy was all alone. To have people leave work and be here is very meaningful," Mr Caloud said.

"We are very content he is buried with his fellow soldiers."

Families of other, recently identified soldiers have been able to choose burial sites, usually in the United States.

But Mr Caloud's organisation had to decide on the ceremony for the unknown soldier, he added.

Bones belonging to troops killed during the war are regularly unearthed. US and Canadian World War I soldiers are being buried at two sites in northern France this week.

Hundreds of new remains are expected to be found as excavation work to dredge a new canal in the region continues.

A new cemetery to hold the influx of freshly discovered remains is being built in the village of Loos-en-Gohelle with a capacity for 1,200 graves.