To persuade Vietnam to withdraw the offer, Western negotiators led by the European Union and Britain have repeatedly increased the amount of money offered to Hanoi.
Half the funding for the final deal would come from the public sector and the other half from private investors, the sources said, declining to be named as they were not allowed to speak to the media.
One of the sources said that only a small part of the money would be provided in the form of grants, while most of the public investment would be in loans.
Western countries have pushed for funding for projects such as offshore wind farms and upgrades to the national power grid.