[johnb838]

Seems to me there are two possibilities:

1) There was no attack and they are saying there was, for reasons known only to them at this point,

-- or --

2) There was such a huge explosion or explosions that they can't plausibly deny it and as such are minimizing it and saying it was outside the city in the desert.

Either way, about all we can know is that whatever the truth is, what we're hearing from Iranian State TV is not it.

[Patriot623]

Heres a 3rd possibility. Too much attention went to Syira after the Iranians planned the bombing in Beirut, so they saw things werent going their way and distracted everyone.
(This of course, infers that the Iranians were behind Beirut)

[Deguello]

"such a huge explosion or explosions that they can't plausibly deny it"

It wasn't that long ago that they had a train carrying munitions explode. They tried to cover this up.