The anonymous air force man claims to have a recording of the operation he alleges involved three other fighter jet pilots.
But he claims to have been sworn to secrecy by the Singaporean government who allegedly told him he will face the death penalty if he speaks a word.
The remarkable claims have been made in a report to the US-based Mutual UFO Network (MUFON), which is the world’s largest organisation dedicated to UFO and alien research.
The alleged whistleblower has given himself the pseudonym John in the report and there is no way of verifying if he is a genuine pilot or not at this stage.
He said in the report filed yesterday: “My life is in critical danger.
“Disobeying a direct order from my superior would cause me the death penalty. I hope you understand how urgent and serious this incident is.
“I will only had over hard copies of the evidence you need to see and not send this over the internet as I am not sure who else is watching.”
He claimed to be part of the Republic of Singapore Air Force.
The pilot added: “Just this morning at 5.20am hours Singapore time, we were given orders to scramble our F15s to intercept a strange looking orb that kept on appearing and disappearing on radar by command control.
“This object entered Singapore air space at around 5.20am and was hovering for at least two hours before 7.30am.
“It is difficult to explain, it kept on appearing and disappearing and re-appearing on another part of our air space.”
He said there were three other pilots were required to “intercept this orb like thing or whatever the hell you want to call it”.
He said: “In fact, when we landed at Changi Air Base, we were given orders by command not to reveal this incident to anyone.
“I cannot in good conscience give you my real name over the internet, but give me your number, I will call you directly.
“I have evidence of the chase itself, I am willing to hand this over to you, a recording of the entire incident between air traffic ground control and the four pilots including myself while in pursuit of this orb.”
The Singaporean air force does use F15s and the pilot has named a legitimate air base.
MUFON will investigate the claims, but has previously said that it is hit by several hoax reports which come in from all over the world.
Sceptics are not convinced by the report and have suggested if the pilot was concerned for his safety he would not have posted it on a database which can be seen online by anyone anywhere in the world, and would have contacted MUFON directly.
Scott Brando, who runs hoax busting website ufoofinterest.org told Express.co.uk: “This looks like a joke.”
Nigel Watson, author of the UFO Investigations Manual, said: “A UFO that is seen for a long time in the same area of sky, generally indicates that it is a star.
“Besides a star we might also wonder if a drone or drones were responsible for this activity, or it is just a hoax report?”