Major US airlines have banned rechargeable battery shipments, as new government tests confirm that explosions and violent fires are likely to occur when large numbers of batteries enclosed in cargo containers overheat.

Citing safety concerns, United Airlines on Monday informed its cargo customers it no longer will accept bulk shipments of lithium-ion batteries. Delta Air Lines quietly stopped accepting bulk shipments of the rechargeable batteries on 1 February. American Airlines stopped accepting some types of lithium-ion battery shipments on 23 February, but it is continuing to accept small packages of batteries grouped together or “overpacked” into a single cargo container.