A military judge has refused to dismiss the most serious charge facing Bradley Manning, the US soldier who allegedly leaked thousands of secret documents, BBC News reported.

Lawyers for the 25-year-old argued there is no proof he "aided the enemy", a charge carrying a life prison term. Prosecutors have argued he "systematically harvested" documents eventually seen by Osama Bin Laden.

The case, allegedly involving 700,000 files, is considered the largest-ever leak of secret US government documents.

"He [Pte Manning] was knowingly providing intelligence to the enemy," said Judge Colonel Denise Lind at Thursday July 18 hearing in Fort Meade, Maryland.

The decision does not exclude the possibility of Pte Manning being ultimately acquitted of the charge.