As for the "justified " kidnapping of Israeli soldiers,

"The taking of hostages is forbidden, both in internal conflicts (Convention I, Art. 3, Sec. 1B and Protocol II, Art. 4, Sec. 2c) and international conflicts. (Convention IV, Art. 34 and Protocol I, Art. 75, Sec. 2c)

In international conflicts, the taking of hostages is considered a grave breach of the Geneva Conventions. (Convention IV, Art. 147)

Also see the 1979 International Convention Against the Taking of Hostages."