How do Allies attack convoy stockpiles by air attack?

[RPKUPK]

At turn beginning I'm getting reports saying that convoy was attacked by Allied air forces with loss of Axis (20) stockpiles.This is happening at hex 124,16 (Casablanca) in North Africa after Vichy North Africa surrendered, but Axis forces are on their way for occupation from the Algiers area. No Allied combat units are visible in North Africa.
How does this occur, what is happening?
Evidently, it's non-submarine activity. How does one attack convoy lines by air??

[Twotribes]

Fleets can interdict ports and cause supply loses.

[Twotribes]

I believe air Units can too. if with in range.

[RPKUPK]

That makes sense except this is occurring at Casablanca, owned now by Axis as Vichy N. Africa just surrendered, but not yet occupied. No trade convoy line there. It is a coastal port hex only. No Allied unit visible (not unexpected). Perhaps an unspotted Allied bomber in Gibraltar bombing a port?!

[AlvaroSousa]

If there is a bomber in Gib then yes.