Although Israel has intercepted several shipments of weapons to the Palestinian territories, workshops in Palestinian territories are building longer range rockets. This is a trial and error process, using whatever materials can be scrounged up and older North Korean artillery rocket designs as a guide. Israelis fear that the "Qassam" home made rockets could reach a range of 5-10 kilometers and endanger critical targets like military and civilian air ports. If that happened, Israel would  probably be forced to reoccupy all Palestinian territory and go building to find and destroy the weapons workshops.