In this case, where the planes struck a mosque near a school, the IDF quickly issued a list of the 19 killed and their positions in Hamas and Islamic Jihad:
Six of the terrorists eliminated were members of Islamic Jihad.
Today, Islamic Jihad denied that there were any of their members in the mosque. Or at least that is how Arabic (and Turkish) media are reporting their press release.
But the terror group used unusual language in its denial.
Their press release said, "We categorically deny the enemy's claims of the 'presence of armed men' from the ranks or fighters of Saraya al-Quds in the Al-Tabi'in School where the enemy committed a horrific massacre yesterday."
Their use of quotes around "presence of armed men" makes it sound like they are quoting the IDF, but the IDF announcement used the term "terrorists," so the Islamic Jihad language is not a quote.
Moreover, whenever Islamic Jihad refers to its members, it calls them "mujahadeen," not "armed men" ("musalahun"). Doing a search for "musalahun" at their Palestine Today website, the term only refers to criminals (and Israeli settlers,) never their own members.
It seems possible that Islamic Jihad is denying that their people literally carried weapons into the mosque while not denying that they were mujahadeen/fighters. They wouldn't hesitate to directly deny that any of their members or fighters were killed if they really weren't; their use of unusual language of "gunmen" in their denial appears to be a deliberate attempt to avoid lying while pretending to deny.
It is also possible that they are translating the IDF's use of "terrorists" as "militants," which is the same word as "armed men" in Arabic, and therefore denying that their members in the mosque are terrorists without denying their presence.
Either way, they certainly didn't deny that these six members of their group were dead!
My impression is that Islamic Jihad is more sensitive to not explicitly lying than Hamas is (and much more than Fatah is.)
In this case, their carefully chosen language in their denial actually supports the Israeli claims more than they refute them.
(h/t Ibn Boutros)