The Pentagon's Defense Security Cooperation Agency, which oversees foreign military sales, notified US lawmakers late Monday about the possible sale, said the source, who was not authorized to speak publicly.

Lawmakers have 30 days to block the sale, though such action is rare since potential deals are carefully vetted before any formal notification takes place.

The approval allows Saudi Arabia and the US government to negotiate a formal contract for the ships, but that process is not expected to be completed before the end of the year, according to a second source who is familiar with the matter.

News of the notification was first reported by Bloomberg.