PICTURES: What are the trails in the sky above Dundee today?

Locals in Dundee were left stumped when a series of odd trails were spotted in the blue skies above the city earlier today.

People took to social media to ask what the cloud-like patterns were.

This image was posted to our Facebook page by reader, Stephanie Burns.

Dundee Airport speculated it was most likely the result of an air display or race, and could have been caused by six aircraft turning in unison at the same time.

There appears to be an air display or race in the sky above Dundee this morning 6 aircraft all turning at the same time! pic.twitter.com/54ELjwZdEQ

— Dundee Airport (@DNDAirport) May 4, 2017

However it was revealed to be the result of American military jets, F-35s, passing over the city as they headed back to their homeland.

As they did so, they sent “sector strips” to local air traffic controllers, according to NATS.

F35s on their way back to the States, sending out sector strips to our controllers another task on our "desk" role!

— Scottish Information (@NATSScotInfo) May 4, 2017

Check out the images of the trails posted by readers.