More than 100 million vehicles are likely to be subject to global recalls linked to faulty air bags made by Takata Corp., up from the current 60 million units, sources close to the matter said Friday.

The National Highway Traffic Safety Administration (NHTSA), the U.S. road safety regulator, is leaning toward a decision to expand vehicles to be covered by the recalls, probably in May. If the move is carried out, the total recall costs are estimated to exceed ¥1 trillion ($9.3 billion), the sources said.

Such a move will deliver another blow to the Japanese auto parts supplier, as automakers have been recalling numerous cars globally since 2008 due to fears Takata air bag inflators could explode with too much force, spraying metal fragments at drivers or passengers.

According to the sources, the NHTSA has so far only sought recalls of some Takata air bags using ammonium nitrate inflators without a drying agent. But it is considering seeking recalls for all of them.

The NHTSA is expected to react stringently against the use of the chemical compound without a moisture-absorbing desiccant, because it is seen to have played a role in the violent ruptures of the air bags.

Takata and Japanese automakers are in talks over how the recall costs should be shared. But the talks are showing little progress and observers believe it will become even more difficult to reach an agreement if the number of vehicles subject to recalls increases.

The move may also lead Honda Motor Corp. and other carmakers to book massive losses.

Mazda Motor Corp. said Wednesday it booked an extraordinary loss of ¥40.7 billion in the business year ended March 31 for air bag recall costs, apparently taking into account that the recalled vehicles could increase.