(Adds Singapore Airlines' ban, comment from Australian regulator; changes dateline)

WASHINGTON/SYDNEY, Sept 9 (Reuters) - Airline passengers should not turn on or charge their Samsung Electronics Co Ltd Galaxy Note 7 smartphones during flights or stow them in checked baggage due to concerns over the phone's fire-prone batteries, the U.S. Federal Aviation Administration said.

The FAA said on Thursday it "strongly advises" passengers to follow its guidance "in light of recent incidents and concerns raised by Samsung about its Galaxy Note 7 devices."

The South Korean manufacturer announced last week it was recalling all Galaxy Note 7 smartphones equipped with batteries it has found to be prone to catch fire.

On Friday, Singapore Airlines Ltd became the latest carrier to ban use of the phones during flights, following an identical move by three Australian airlines.

"The powering up and charging of Samsung Galaxy Note 7 mobile phones is prohibited on all our flights," Singapore Airlines said in a statement.

On Thursday, Australia's Qantas Airways Ltd, Jetstar Airways and Virgin Australia Holdings Ltd announced they had banned passengers from using or charging the phones in response to the recall.

Although customers will still be able to bring the phones on flights, the bans extend to the phones being plugged into flight entertainment systems where USB ports are available.

Australia's aviation regulator said on Friday it is working with airlines and foreign aviation safety regulators "to ensure that recalled devices are treated and carried safely."

Delta Air Lines Inc, the No. 2 U.S. airline by passenger traffic, said it is still studying the issue.

"Delta is in constant contact with the FAA and other bodies in its run of business as a global airline. We will comply with any directive and are studying this matter. Safety and security is always Delta's top priority," spokesman Morgan Durrant said in a statement.

United Continental Holdings Inc and American Airlines Group Inc did not immediately respond to requests for comment on the FAA advisory.

Vaughn Jennings, a spokesman for Washington-based trade group Airlines for America, said the organization was "closely monitoring any developments as this issue evolves."

"Each individual carrier makes determinations, in compliance with FAA safety rules and regulations, as to what is permitted to be carried on board and in the cargo hold," Jennings said in a statement.

The FAA statement does not order U.S. airlines to take action.

The International Air Transportation Association said airlines have conducted risk assessments and noted that other phones have been recalled for battery issues.