NBN costs balloon as Malcolm Turnbull says further $15bn may be needed

The communications minister maintains earlier figures were known to be unreliable as they were based on inadequate financial information

The costs of building Australia's largest infrastructure project, the national broadband network, could rise by as much as $15bn according to a new corporate plan released on Monday.

The communications minister, Malcolm Turnbull, acknowledged the forecast costs associated with the project had risen as he released the new corporate plan of the NBN Co - the company overseeing the rollout.