coffinman as David said Meir Amit can be a useful source as long as you do not make the mistake of thinking they are in anyway a neutral one. The fact they renamed themselves in memory of Meir Amit who was an Israeli General, politician and head of Mossad and Wikipedia descibes the site as
The Meir Amit Intelligence and Terrorism Information Center, formerly The Intelligence and Terrorism Information Center, is an Israeli NGO. It was renamed n honor of Meir Amit.

The Center is directed by former Military Intelligence officer, Dr. Reuven Ehrlich.[1] The center is often regarded as being the "public face of Israeli intelligence."

The Centers research staff, mostly former Military Intelligence officers, compile weekly reports that are published online www.intelligence.org.il
should give a clue as to its leanings. As to the 13 groups they had not commented when I looked. Hamas may not be one of them as it usually tries to suppress the other groups desire to attack the occupiers as it knows it, and the civilian population, will bear the brunt of the reprisals as the only group with identifiable assets.