From The Portal Raids:
The commodore knew his duty, and though his office required him to remain stoic, he knew he was showing mercy in issuing his next order. The squadron might have had insufficient crew to launch a defence of the city below, but it could certainly intervene, as well as granting a quick death to those who would otherwise not receive any such fate. Minutes later, the skies of Aventine were split by the black entry containers of a hundred orbital plasma warheads. Each detonated with the power of a star, burning to ashes every last alien within a hundred miles as well as the captives they were attempting to drag through their dimensional portals.
That day, Commodore Kybras demonstrated that Mankind could be every bit as cold-hearted as the cruellest of Dark Eldar, if the Emperor so willed it. That it might have poisoned Aventine’s populace against the Imperium and lead to the rise of even greater threats would be a menace for another day.