U.S. fighter jets escorted two commercial airliners to Atlanta's Hartsfield-Jackson International Airport on Saturday after "credible" bomb threats had appeared on social media, the Atlanta Journal-Constitution reported.

Once on the ground, FBI agents and a police bomb squad searched the planes operating Delta Air Lines Flight 1156 from Portland, Oregon, and Southwest Airlines Flight 2492 from Milwaukee, Wisconsin. No threatening materials were found on board, the newspaper said.

"We believe the threats to be credible," airport spokesman Reese McCranie had noted, though authorities have not said what exactly led them to evaluate the warnings in that fashion. FBI spokesman Stephen Emmett, meanwhile, said that NORAD -- the North American Aerospace Defense Command, which is responsible for the defense of U.S. airspace -- scrambled the fighter jets.

The threats apparently resulted from two tweets by Twitter user @kingZortic, the Verge detailed.

"I have a bomb on one of your planes, but I forgot which one when I left the airport. Can you help me find it?" the user wrote directed at @DeltaAssist, the airline's customer-service account. "It was from Portland to Atlanta, I forgot the flight number, though. It was something like DL156 or DL 1556. I forgot the order," the individual continued in a second message.

In additional messages, @kingZortic gave additional details, according to the Atlanta Journal-Constitution.

"It was smuggled through one of the back entrances because the airport didn't have much security around one of the entrances so the bomb is at the back of the plane," the user wrote. "Everyone will know when it's detonated."

The account also specifically mentioned the Southwest flight from Milwaukee.

"A bomb was placed on SWA2492," a message read. "It will be detonated at a random time of my choosing. If anything happens to me I'll make sure that more flights are targeted. I strongly suggest you don't try anything stupid."

Authorities, however, have not confirmed the link between the tweets and the bomb threats, the Verge cautioned. They were published while the flights were still in the air, the website added; the account in question, meanwhile, was suspended by Sunday.

Fliers had to endure a long wait on the tarmac while authorities ensured that it was safe for them to disembark. The pilot gave updates every 10 minutes, sent the beverage cart through again and allowed bathroom breaks, Southwest passenger Toni Ellingen said.