There were no explosives found on two passenger jets that were escorted to the main airport in Atlanta by American fighter jets.

A full-scale investigation got underway after bomb threats were made against the two passenger planes yesterday.

The flights landed safetly at Hartsfield-Jackson International Airport.

The threats against Delta Air Lines flight 1156 - coming from Portland, Oregon - and Southwest Airlines flight 2492 - from Milwaukee - were deemed credible.

It is believed both airlines received the threats on Twitter.

An explosive squad and dog unit searched both of the aircrafts.

The planes were escorted back to the airport by fighter jets.

A spokesperson for Southwest Airlines said yesterday: Ddue a security situation, the aircraft operating Flight 2492 was taken to a remote area of the airport where customers and the aircraft are being rescreened. Our number one priority is the safety of our customers and people. We cannot comment on the nature of the security situation."