Sources say the three men were not part of the foreign fighters unit that was being trained at the now destroyed Yavoriv base, which is just six miles from the Polish border.

It is not known which branch of special forces they had served in.

As many as 30 cruise missiles were unleashed on the base, 35 miles from the western Ukrainian city of Lviv where thousands of refugees have flocked to.

Asked in the aftermath of the devastating blasts on Sunday if British casualties were among the dead UK Foreign Office sources said they were unaware of any.

The British MoD confirmed there were no serving personnel killed or injured in the explosions.

A source told the Daily Mirror: “There were many more killed within the site than has been claimed and bodies are still being found.

“I do not believe the three British ex-military personnel would have known anything about it, fortunately.

“This is extremely sensitive as there are believed to be no serving British military personnel inside Ukraine as politically that would be extremely controversial.”

Witnesses have described how the attack at 5.45am “turned the sky red.”

Hours after the attack, ambulances were still rushing to the scene

Roads leading to the facility were blocked with checkpoints and authorities were conducting search-and-rescue operations.

The base is known as the International “Peacekeeping and Security” Center.