The U.S. Consumer Product Safety Commission and Samsung are urging owners of Samsung's Galaxy Note 7 to stop using their phones while they work to formalize how a recall will work.
The warning comes a week after Samsung announced a voluntary recall of 2.5 million phones worldwide because of a battery problem believed to affect 0.1% of all devices. Some customers reported that their Note 7s caught fire.
A government recall would outlaw the selling of the phone. In its statement, the agency asked owners of the Note 7 "to power them down and stop charging or using the device" in the meantime.
Details on an official recall will come "as soon as possible," the agency said.
Tim Baxter, president of Samsung Electronics America, said the company is collaborating with CPSC and its carrier partners to ensure all Note 7 users are alerted.
Samsung, based in South Korea, has been offering customers a different phone, the Galaxy S7 or Galaxy S7 Edge, and a $25 gift card or bill credit.
The Federal Aviation Administration on Thursday advised airline passengers to not use or charge their Note 7s on board an aircraft and not to stow the phones in checked baggage.