Two US mobile carriers said they will stop issuing Samsung Electronics Co Ltd's new Galaxy Note 7 smartphones due to safety concerns, a further setback for the world's top smartphone maker trying to manage a growing recall crisis.

AT&T Inc said on Sunday it will stop exchanging new Note 7 smartphones due to reports of fires from replacement devices that Samsung has said used safe batteries. T-Mobile said in a separate statement it is temporarily halting sales of new Note 7s as well as exchanges.

Samsung in September announced a global recall of at least 2.5 million Galaxy Note 7 smartphones, its flagship new device, in 10 markets including the United States due to faulty batteries causing some of the phones to catch fire.

A Southwest Airline flight was evacuated earlier this week after a replacement model Note 7 smartphone began smoking inside the plane.

Samsung shares were down 3.7 percent as of 0042 GMT, compared with a 0.1 percent fall for the broader market.

Samsung said it was investigating reports of "heat damage issues" and would share its findings when the investigation is complete.

"If we determine a product safety issue exists, Samsung will take immediate steps approved by the CPSC (U.S. Consumer Product Safety Commission) to resolve the situation."